There is no such law for a merchant. There is such a law for a DEBT. Legal Tender must be accepted for a debt, both public and private. Legal tender can be a jug of 50000 loose pennies. As a merchant, when you come into my store and select an item for purchase, that is not a debt. I can choose to accept or not accept any method of payments as a merchant. I can accept only silver or gold in exchange for my goods if I so choose. Your Mortgage payment or electic bill is a debt. You may pay that with any form of Legal Tender. Ebay CAN dictate what forms of payments are accepted. You don't have to shop or sell there if you don't like thier terms.