I saw one foreclosure that failed to close because it was a shill bidder. He started bidding at about 375K and kept raising and then dropping out until his last bid was not advanced and he won the auction at 825K. Then he failed to close the deal and the property had to be resold. The price dropped from 800K plus to just over 400K on the resale. We knew what had happened and the second and third highest bidders both refused to take it at their last bid and both refused to bid at the resale.
Not only that but the second highest bidder, who buys and sells a lot of property in the area, explained to the auctioneer that a repeat of that shill bidding might be a very bad idea. Lawyers are cheap and the charge of rigged auctions will damage a auctioneers reputation beyond repair in small towns.