That is untrue. No corporate in real world saves employees' SSNs in an
offline server, in fact, it is not a safe way to store such sensitive
information. Also, eBay sellers are not eBay employees.
No, it's not safe to give them away your SSN. Your bank account can be
replaced anytime, but your SSN cannot be. They have no business to have
your SSN anyway. Plus, you are already paying one of the highest selling
fees by selling stuff on eBay.