[Cozumeleno]

Can't speak to traditional auction houses when it comes to this but as someone who used to sell bulk lots of eBay, I'll give my two cents.

It's difficult because card thickness varies. (500) 1990 Upper Deck is different than (500) 1934 Goudeys. So while I consider about a 5% variance to be a good number, I don't know how hard it would be to complain about 10% for a large transaction. 20%, as it seems in your case, is unacceptable, though - especially considering that 800 cards isn't a ton and that it's easy to tell that 500 cards, unless ultra thin, won't fit into a 400-card box.

Since it said 'approximately', I don't know if you technically have a valid beef. But I'd at least let them know about it and see if they will do anything.

And FWIW, I once was in the same boat with a lot on eBay. The seller took the difference and refunded me the per card difference that I bid. So if you paid $100.00 for 1,000 cards, you'd get a $20.00 refund, assuming there were 400 cards. Not saying they will do that, but it's a reasonable solution.