any ideas for old book pricing??

Both my boss and my neighbor have a ton of old, quite possibly antique and expensive books. In the neighbor's case, she just wants to sell them, and in the boss's case, she needs to get a basic idea of how much each is worth so that she can decide which to sell and which to keep as library assets.
anyway. The boss is currently using abebooks for this research, and has asked me to "put out a query to all your online book people" to see if this is close to accurate, or if there is some other source online that she can at least get a second opinion from. I'm looking for the same info for my neighbor, basically just wondering if abebooks is an accurate place to go to begin with?

any comments, suggestions, help???

See what similar or identical things go for on ebay.

I would also recommend ebay as it is a better idea of what people will actually pay for an item vs. what an item is being sold for.

There are a few out of print books that I'm after and both Abe Books and the Amazon marketplace sellers agree on prices. Unfortunately those prices are hundreds of pounds, but I'd say that Abe is a safe bet.

At my local used, I came up with a bunch of old hardcover books the owner had misplaced long ago. So I was upset when he ended up taking William Golding's Darkness Visible away from me to price it more accurately, but at least now I can tell you there are such websites out there that will tell you prices depending upon the edition and condition.

Perhaps I'll stop by and ask.

Abebooks gives you an idea of a used or rare book's retail value. Most of the listings are entered by professional booksellers, after all, so you're going to get the high end of price ranges--always higher than the price that an individual will get when selling a book herself.

However, if your boss is trying to value a collection for tax or insurance purposes, the prices at Abebooks would be useful; though if the collection is big, it would be more efficient to bring in an appraiser.