More information is needed. Was there a written contract? What did the contract say? Did it include an disclaimer of warranties? What did the salesperson say about the coins? What state were the coins purchased in?
NOTE: This answer is not intended to be legal advice and should not be construed in that way. This answer does not create an attorney-client relationship and no such relationship may be created absent a signed retainer agreement. The author is licensed in Illinois only, and his answer is for educational purposes alone.