IMO, bad idea. eGay will catch all of you and ban all those accounts. Think about how many people have ebay accounts. Now even if your 'group' had 100 members there would have to be considerable overlap between all the accounts.
If A bids on on multiple auctions from B, it will eventually look very strange. Haven't you ever read seller's feedback and a buyer is asking whey so and so keeps bidding on your auctions. You could get away with this sort of arrangement years ago, but I think you are asking for trouble. It is too easy to track.