Feedback is important. You have to send a message sometimes by deleting a high negative feedback bidder. I would never bid against someone who has a string of negative feedback for non payment (he doesn't care what he bids it up to). I've also emailed a few folks that had items for sale to let them know that I refused to bid against someone that had a lot of negative feedback and told them that there were other paying bidders that felt the same way!
Its up to the user to control the atmosphere. Use the feed back. If a person gets below -2 feedback, Ebay bans him. It is harder to get an account now than it was in years past. You have to identify yourself via the same type of credintialing that a loan would take. (ie CC and checking acct as well as ssn). It is hard to fake a ssn with a CC or checking acount to go along with it.
If you see abusers, let them and the person with the auction know. The seller wants to make money. If they think that they are going to loose big time and have to relist the item or possibly miss out on the bid amount going higher, they'll drop the dead beat in a hurry.
As for the person running up their own bids, If you see that, contact that square trade group. If it is true, theyll kick them off. I've seen people get thrown off of Ebay before. I was bidding on a computer part and all of the sudden, I was the high bidder. I went into the bid history and saw that the person that had been winning the auction was no longer there. There was a reason given in the comment field that Ebay had removed the bidder for some continuouse infractions. Ebay wants to keep making the bucks that they do and they know that they have to enforce the rules in order to keep things even. Its there fortune also.