I have not used auction.com but am considering it and have read through many of these negative reviews. Here's my attempt at separating what are real versus fake concerns.
But first I need to point out the obvious: the point of auction.com, like every other auction site, is to get the highest price possible for the seller. It is NOT to get you the best deal. If you get this backwards you will probably have a bad experience.
Common fake complaints:
They don't show the reserve: Think about this... what would your opening bid be if they did? The reserve amount of course. By not showing it there is a chance you will bid above the reserve right off the bat. Remember the main point is to help the seller, not you. BTW, eBay has been doing the same thing for years.
The site bids against you: This is one of the first things disclosed on the property's auction page. If you're bidding tens, if not hundreds of thousands of dollars without knowing how this works upfront, you're being very foolish bidding in the first place. This is the logical way to manage the reserve not being published. You may not like it, but it make sense.
Time added to the auction: Another common practice with online auctions. Remember the original point. Any auctioneer's goal (live or online) is to maximize sale price, not get you a great deal. Sites often have rules that say they will add x minutes after the last bid to solicit a higher bid. They want to keep the auction going as long as possible to keep the bidding going higher. If you're upset over this, you don't understand auctions.
Reserves too high/closing was a hassle: These are not the site's issues. You are most likely buying a REO (real estate owned) from a bank that has completed the foreclosure process on the property. It is a painful process. PERIOD. They are a pain in the neck to deal with. If you're trying to get a screaming deal by buying this way, the hassle factor is part of the price you pay.
Real complaints:
Poor customer service / rude agents: These could be absolutely true since no organization is perfect here. But also remember that these agents can be a reflection of the people writing the reviews. Think about it this way. The winning bidder calls the site's customer service because they're already frustrated that they can't get the deal completed. But the agent doesn't have any control over the bank or reo company to keep things moving. Everyone is going to end up frustrated in the scenario.
Hope this helps some of you to decide whether or not you want to try the site.