If I remember right, ebay has no rules about having several ID's, as long as you aren't bidding on your own items. Sounds like that is what is happening here; you might also send them a message about why you don't want them bidding on your stuff. They might be confused why they can't bid and trying another ID because of that, lol...on the plus side, you'll have all their ebay IDs if they keep this up, in case there's ever a problem?