Here is another example of why catalog value is a guide and not an absolute.
Case #1. Suppose you have 1 million used Forever stamps. At a minimum catalog value of 20¢, there is $200,000 of catalog value. If you tried to sell that accumulation of 1 million stamps to a dealer, most dealers would say “no thanks.” Any offers you did get would be for a tiny fraction of catalog value.
Case #2. You have a copy of Scott #C3a. The catalog value is $250,000. Your copy is in superior condition: never hinged, no faults, and perfect centering. I have a buyer who is willing to pay $500,000 immediately for that copy. I will buy it from you for, say, $490,000. I’ll sell it instantly to my waiting buyer. Assuming I don’t lose the stamp or damage it while I have it, there is no risk on my part.
In case #1, you have lots of very common stamps with almost no demand. You’ll have a difficult time selling them at any price.
In case #2, you have a very desirable stamp with huge demand. This stamp sells instantly at almost double catalog value.
These are two very extreme cases. Most collections fall between these two extremes. When it comes time to sell, what can you expect? Sorry, there is no formula that can pinpoint an exact figure, or even estimate a ballpark figure.
The more stamps that you have which are very common and in low demand: the offer price is going to be a small percentage of catalog value, especially if there are a lot of duplicates. The more stamps you have which are sound and in high demand: the offer price is going to be a higher percentage of catalog value, and perhaps even over catalog value.
When someone says to me, “I want to sell my collection for 35% of catalog value,” that means nothing to me. If you have a lot of common material or items that are heavily damaged, 35% is too high. I’m not interested. But if you have superior material that is in demand, you’re asking too little for your collection. It’s possibly worth more. And I’m probably very interested.
Sales are completed when the stamp dealer and the seller can agree on a price. In my experience though, working with just a quote from the catalog value isn’t how sales are successfully made.