I used to look for these a lot back on eBay's forums back in the day when they were still big on having community help solve a lot of the issues around the site. I ended up earning around $30 worth of eBay credit for some of the work I was doing, oddly enough!
Now I'm sure things have changed over the past four years, but it used to be that people who did shill bidding were quite stupid. They would use a secondary and tertiary account to bid up their own auctions. They would also have the audacity to leave feedback for themselves with these other accounts as well, making tracking them quite simple. If a Buyer or two only buys from one particular Seller, does so dozens of times, and is involved in bidding on more than 50% of the auctions, you have multiple red flags waving in your face.
Unfortunately, we all pointed out to eBay way back when that most people did this because the worst punishment available was striking those accounts off of eBay. The only problem was that these Sellers would just create two or three new accounts minutes later and start all over again. It's pretty bad when I can link over 20 different accounts to one another over a two week period and 17 of them were NARU'd fairly quickly. If I can see that pattern in less than ten minutes of searching, why didn't eBay care? We all presumed that the answer lay in the fact that, despite shill bidding, eBay was still getting all of the after-auction fees regardless. They weren't reimbursing Buyers for getting screwed, they weren't penalizing Sellers for pulling fast ones. They pocketed whatever fees they got from the auctions and that was pretty much it. What was worse, asking any employee who worked the boards about it resulted in an immediate shut down of the thread without any reasoning whatsoever. Peculiar, no?
In the end eBay basically kicked all of us investigators out because they felt we were causing more trouble for their Power Sellers based on information that may appear to be true but, in reality, wasn't true. Peculiar as well considering that we tended to put a few bucks in here and there and found out that dozens of particular crooks and shill bidders had the same names, addresses/PO Boxes, states, and zip codes as others! Some were "relatives" of the same people...with the same addresses, same "check out" info, exactly the same product listings (letter for letter)...hmmmm...
Just be careful out there. eBay was quite unscrupulous before, but at least it was mostly behind the scenes where nobody really noticed since ripoffs weren't rare but they were being handled. Now? Ooooh...caveat emptor.