We bought our flip from www.ushomeauction.com (company is called REDC). They add 5% to the winning bid tho, and the 'winning' bid still has to be approved by the lender (the bid may fall below their reserve price so you walk away empty handed). In our case it worked out, but just giving you a heads up on how it works.
BTW the opening bid means nothing. Ours had an opening bid of $500 and we bought it for $105K (plus $5,250 in auction house fees).
Some areas of town went for 50-60% of former retail value, some went for 90%. So it depends on how desirable the area is.