A lawyer for Tiffany & Co. accused eBay Inc. on Nov. 13 of allowing the sale of tens of thousands of pieces of counterfeit Tiffany jewelry on its Web site; an eBay lawyer responded that Tiffany wasn’t doing its share to protect customers.

The arguments in U.S. District Court in Manhattan came at the start of a trial to decide whether eBay can be blamed for the sales of silver Tiffany knockoffs on its Internet site since 2003.