You can report the cost basis as being more than the sales price if you can substantiate that assumption by producing documentary evidence. If you get audited, it is unlikely your assumption would be adequate if you had "no way of knowing."
The cost basis of property you received as a gift would be the cost basis of what it was in the hands of the donor, or it's fair market value, whichever is less. So, if you are dealing with collectibles that went up in value during the time the donor owned it, you likely have income upon it's sale.
@colby_parker
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
