EBay Inc. might be violating false-advertising laws if it does not warn consumers that some items billed as upscale jeweler Tiffany Co.'s products by sellers on its Web site are not authentic, a federal appeals court said Thursday.

But online auction site operator eBay won significant victories in rulings by the 2nd U.S. Circuit Court of Appeals that said it did not engage in trademark infringement or trademark dilution in its use of jeweler Tiffany & Co.'s trademarks. Those rulings upheld the findings of a lower court judge.

Tiffany sued eBay in 2004, saying eBay engaged in trademark infringement, trademark dilution and false advertising because most items that sellers list for sale as genuine Tiffany products on its sites were fakes.

The appeals court left in place a finding by the lower court that eBay did not violate false advertising laws but returned the case to the judge to consider that issue again.

The three-judge panel said in its written ruling that it had difficulty with the lower court's reliance in its ruling on eBay's assertions that it did not know which listings offered counterfeit Tiffany goods. The 2nd Circuit noted that eBay advertised the goods sold through its site as Tiffany merchandise.