I went to my first auction many years ago and was surprised to see sellers bidding on their own machines. They were often the winning bidder. I was told this was a "buyback" and was normal at pinball auctions. In the case of a "buyback", the seller pays some small fee for auctioning his machine but doesn't have to pay any of the fees a real buyer would be charged for winning an auction.
There were quite a few sellers at that auction and some were willing to let their machines go at good prices so it still seemed like there were deals to be found.
If there is only one seller at the auction and he has a reputation for wanting retail + for his games, chances of getting a decent value, let alone a good deal, are practically nil.
I don't see how not having a reserve makes any difference to the buyers when the sellers are allowed to bid on their own machines. Seems like it just makes it easier for the seller since he doesn't need to be present and actually bidding to insure he gets his required minimum price. I suppose it's also a good marketing ploy to be able to advertise it as a "No Reserve" auction since many people are familiar with the term on Ebay, where it actually means something.
One thing that is often missed when you look at a list of hammer prices after the fact is the true condition of the game. This can be difficult to determine even when you're at the auction. It was rare if you could open the backbox to see if the boards were hacked or even all there on non-functioning machines.
I was surprised at how much people were willing to bid on machines without being able to open them up and inspect them fully.
Edit: Was writing my post as Jwo825 was posting his. Almost identical thoughts.