Posted By:
Tim NewcombIn this hypothetical, you have been offered the cards free and clear even though you have told her they are valuable, correct? Assuming she is of sound mind, it appears that you have no legal obligations. But I agree that some form of reimbursement seems fair.
Seems like you could do a couple of things:
1. If you were going to sell them through an auction house: take them now on a sort of consignment basis and tell her you will give her a percentage (50%?) of what they bring. You could draw up a simple contract on that basis, I guess.
2. If you would prefer to keep them for your own collection: insist that she take a substantial amount, say $2000-2500, which would help her out but still give you a good deal. In this case I think it would also be fair to then sell some of the cards to recoup your outlay, as long as you kept the bulk of them.
3. Don't call Al Rosen 
Good luck--
Tim