Right off the top of my head, that sounds like a fairly reasonable offer. Even if you're not planning on selling them on e-bay, that is a good place to get a rough value of their worth. If you do so, however, you need to check the completed auctions to get the price that things actually sold for, rather than current auctions. Also, as with many things, there are probably a few cards that have more value, so sales of individual cards wouldn't be particularly informative. You would need to look for collections of about the same size and age. I suspect that they are a bit like old family photos. If I had a thousand old family pictures of various people I didn't know, there wouldn't be a lot of economic value. The value is to the people with some connection. Fortunately, with QSL cards, it's quite possible to find the history of the person(s) involved. I suspect that there are a lot of people who would be interested in obtaining an old QSL card of a family member, or perhaps of the former holder of their callsign. If someone had a large collection, it seems to me that the best way to sell it would be to post it somewhere on the internet so that the text is searchable. Then, when someone does a search for their grandfather's old callsign, they will be able to see his card for sale.