you can report it to ebay.
i had the same bother once. i let my boyfriend use my account to buy something, he had never used ebay before so wasn't really clued up on it all.
but his item never arrived and he was emailing the seller asking questions and they then started sendng abuse back.
once i knew what was going on i forwarded everything on to ebay and the persons username and ebay got back to me saying they were sorry and were dealing with it but couldn't let me know what had been said to the other user due to privacy, rules etc