I've Inherited This Collection...
I get frequent emails from people who have inherited collections of one kind or another, asking for help in figuring out what they're worth or how to dispose of them. This is a very difficult question to answer, so I've taken the time to write up some loose guidelines that you can follow.
To All You Collectors Out There
I want to start by making a plea to all of you collectors who have read this far. PLEASE PLEASE PLEASE spend the time to document your collection for the benefit of your heirs! So many collectors spend decades building great collections, only to have them completely wasted when their heirs dispose of it by selling it to a pawn shop at a tenth of what it's worth. Even worse, I frequently see heirs at shows getting their inherited albums appraised by a dealer, only to get some disappointing number like "50 bucks", and they end up leaving, convinced that the dealer is a scumbag. If you've spent a couple of decades building your collection, you should spend a couple of hours typing up one or two pages which will give your family reasonable expectations and explain to your family exactly what kind of collection it is, what it is worth in real general terms, and what you think is the best way for them to sell it, if they decide not to keep it. I know that you think that your wives or family have listened to your every word when you've talked to them about your hobby, but trust me - they haven't. They've been humoring you. And once you're gone, they won't have a clue what to do with your pride and joy. So take the time to tell them, and make that explanation a part of your will.
Warnings Before You Get Started
OK, back to you inheritors. First and foremost, I should give you a warning, and you should take this seriously - the collection that you inherited is probably not nearly as valuable as you think it is. If you have watched over the spending that went into building the collection, and if you have a rough estimate of exactly how much money went into it, then you have a fair idea of what it's worth (although you will probably not be able to sell it for what it cost to build it). Otherwise, your dreams of selling the collection and buying a new house are probably unrealistic. Almost every time that someone has shown me a U.S. collection and asked what it's worth, my answer has been either "very little" or "just the face value of the stamps". You should prepare yourself for just such an answer.
Warning #2 - NEVER NEVER NEVER sell any portion of a collector to any person who provides you with an appraisal of its worth. This is a conflict of interest which can never be trusted under even the most honest of circumstances. Stamp dealers are a very honest bunch, by and large. But there are some bad apples. And even the honest ones may have no qualms about capitalizing on your ignorance. If you plan to sell a collection, get it appraised by someone other than your intended buyer. The one exception to this is an auction house. Since they will sell your material to the person willing to pay the most for it, there is no conflict in interest in getting an auction house to estimate its worth.
Quick Guide to U.S. Collections
If you've got a U.S. collection, I can give you some quick answers that you can use to set expectations. If a stamp was issued after 1930, is unused, is in great condition, and has a face value below 50¢, it is most likely only worth its face value. If it is used, it is most likely worth less than that. There are exceptions to this, but this is true for most stamps that you are likely to have. The older a stamp is, and the higher its face value, the more valuable it is likely to be. This guideline breaks down almost completely for stamps issued before, say, 1925. But it is particularly true for stamps from the 1940's, particularly the 3¢ issues.
On the other hand, if your collection includes a lot of certificates from organizations such as "Philatelic Foundation" (PF), "Professional Stamp Experts" (PSE), or "American Philatelic Expertizing Service" (APEX), then your collection is probably valuable. Collectors usually don't bother to get a stamp expertized unless it is worth $100 or more. You should take your collection to an auction house (I recommend Shreves, Siegel, Bennett, or Rumsey), as they will give the most honest appraisal, and they will likely get you the best sale price for your material.
So let's get into how you can determine its value. If your collection is a postal history collection (mainly envelopes with or without stamps, showing neat postmarks, unusual designs, famous senders or recipients, interesting letters, and so on), I am going to be of very little use to you. Determining the value of postal history items is difficult and best done by a postal historian, which you and I are not. It may take you some time to find someone who can properly assess its worth, and you may need to ask dealers for referrals before you find someone who can do a good job.
If your collection is just a bunch of stamps stuck in an album (or maybe just in envelopes), your work is much more straightforward, as there are probably several catalogs that you can use to determine their rough value. You need to start by determining the type of collection that you have. Identify the country or countries represented. See if you have unused stamps or used stamps. See if there are a lot of fancy cancellations. See if you've got stamps that just "look wrong" - missing colors, perforations in the wrong place or missing altogether (errors). Once you know the kind of stamps you have, you can track down a catalog that gives the values for those kinds of stamps.
Warning for U.S. Collections
I should probably jump in at this point and say that there was a period of about 20 years where all of the U.S. stamps looked the same. If you are not a collector, you will probably be unable to use a catalog to determine those stamps' values, because you won't be able to tell the difference between two almost identical green 1¢ Washington stamps without learning a lot about stamps. So if your stamps look like these stamps, don't bother finding a catalog. Just go to a dealer. The good news is that it's more likely that your stamps have some value.
So now you've identified your collection. If it is a normal U.S. or foreign collection of stamps, used or unused, your best bet is to track down a set of Scott catalogs. You can find these for sale by most stamp dealers, but they're expensive - about $45/volume. Most large libraries also have a set in their reference collection. A library's copies may very well be a year or two older than the most current version, but that's fine. Your goal is to get a rough estimate of your collection's value, and stamp values usually don't change much from year to year.
If you have a foreign collection, you want to look for Scott's set of worldwide catalogs, which is five or six volumes. Scott's worldwide catalogs include U.S. prices as well, but U.S. collectors don't use the worldwide set to determine U.S. prices. They use a single volume called "Scott Specialized Catalogue of United States Stamps and Covers". A few collectors use a catalog called the Brookman catalog, but I recommend avoiding it. Brookman lists prices which are mainly used for retail pricing. As such, Brookman will give you an inflated sense of value, which is misleading for what you want to do.
Using Scott Catalogues
OK, you've gotten your hands on the appropriate Scott catalogue, and you want to figure out what one stamp's value is. First, you need to find the stamp in the catalog. The catalog is broken into sections - by country for foreign stamps, by stamp type for U.S. stamps (where "type" means "normal postage", "airmail", "parcel post", "savings bond", "revenue", and many others). Within a section or country, the stamps are sorted generally by year. If you know the year of your stamp, that will narrow your search to a couple of pages, and you can just look for photos which match.
For U.S. stamps, Scott (and my web site) offers you some lists which you can use to find stamps more quickly. At the beginning of the Scott Specialized catalog, you will find a Subject Index, which you can use to find unusual subjects, like "Ty Cobb", "Certified Public Accounting", and so on. It arranges stamps by subject and provides catalog numbers, which you can use to find the listing for your stamp. If your stamp is a squarish stamp (often with someone's head on it), it's probably what's called a "definitive" stamp. For this, you can use the Identifier of Definitive Issues, which arranges definitives by face value. If you have a hard time using Scott's guides, you can use the denomination guides on this site (see the menu). I've broken my collection into different types, and I list those types first by value, then by description. So you can find the right type guide, find the stamp's value, and find the listing there. If it's a smaller value (like 1¢ or 2¢), you may want to use your browser's "find" function to search for terms like "Cherokee" or "Cobb". The disadvantage to using my site is I only list stamps that I own. Now I own virtually all stamps after, say, 1925, so my site's fine for identifying newer stamps (but not their values - you can use it to get the catalog number, then go to the catalog to find the price).
One final warning about catalog prices. Scott and other catalog companies assign every stamp a minimum value. For Scott, it is currently $0.20 or roughly twice the stamp's face value for unused stamps (whichever is higher). This does not mean that you will be able to sell the stamp to a dealer for $0.20. Stamps like this - in fact, most stamps with a catalog value of less than $1 - will usually be purchased by a dealer for face value, or even a fraction of face value. They're so common that there is little market for them, and most dealers have several of such a stamp in their stockbooks already.
Adding It All Up
Now, you've used the catalog, and you've started building a running total of your collection's value. What do you do now? Well, you should expect that your collection can only be sold for a fraction of whatever total you reach, depending on a number of factors. If the collection is of unused stamps, it will be worth more if the stamps are in "mounts" (like you see on my pages) than if they are attached to the pages with hinges (small pieces of gummed paper which attach directly to the stamp and to the album page). The quality of the stamps matters too - are they discolored? Poorly centered? Cancelled with heavy marks? I can't give you a pat answer to how much your collection is worth relative to catalog. Most collections are worth a fraction of their total catalog value. The really good collections are worth a multiple of their total catalog (mine is an example of such a collection - I pay multiples of catalog value for my older stamps).
The total catalog value will give you a sense of how you can dispose of your collection. You may want to sell stamps with a catalog value of $5-$50 individually on eBay. eBay is a good place to determine what a stamp or a set of stamps is worth. Once you've identified a stamp, you can do an eBay search of completed auctions to see what similar stamps have sold for. The more valuable and least valuable stamps won't show up - face value stamps aren't worth selling on eBay (usually), and more valuable stamps can be sold for more elsewhere (usually). But the mid-range stamps will be all over the place. Once you've got the catalog number for a stamp, you can use that number and a descriptive term to use Google to search the net for dealers selling similar stamps. If you search for "834 Coolidge", you can find everyone selling the $5 stamp on this page. You can also use eBay and other sites to get a sense of how condition affects a stamp. If you search eBay for "834", you will see every 834 regardless of condition, and you can see how "lightly hinged" differs from "never hinged" or how centering affects value.
And if you choose to sell to a dealer, the total catalog value will give you an idea of the kind of dealer to go to or the level of interest a dealer will have. Smaller dealers will buy a $2000 collection for maybe $500. Larger dealers will travel great distances to examine a collection with a catalog value of $10,000 or more.
It is extremely difficult to provide a general answer to "what is my collection worth?", and I'm only experienced with U.S. mint NH material. You should take everything I've said here as a guideline which you can use to be more informed when dealing with the collection that you've inherited. Feel free to email me more specific questions, and I'll expand on this page as its shortcomings are pointed out to me. Good luck.