I usually do quite OK at the auctions. I stay right next to the auctioneer. That way he sees me first when I toss out that crucial $25 bid. You HAVE to get that in first, otherwise someone else will, and then you are having to bid $50.
My first auction purchase was a working Capcom Bowling with a dead monitor (in a pac-man cabinet). It was the second game of the auction, with the first being a Ms. Pac. The Ms. Pac went for like $900, and everyone was still grumbling about that, and I snatched the Capcom Bowling for $25. Another dead monitor one brought $75, later, and a working monitor one brought $200 at the same auction.
I got a nice "13 video poker for $50, when all the others at the auction were going for $100-$200. They had one row of 19" Cherry Masters with that lone 13" video poker in the middle of them. All the other 13" ones were in a different row. Every one who was watching at the time was going for the Cherry Masters, and thus did not bid on mine. Then when they did get to the row of 13" ones they all went for $100+ (except the ones with monitor problems).
I got my dart machine @ $25 when all the others went for $100 plus. Because mine didn't power up, and the person who won it suddenly realized as soon as they had finished the row, and he backed out. I yelled $25 to the guy writing the prices, he took it, and they moved on. (Adjusted the power supply knob at home, and then it worked fine).
My Assault was $150. I hadn't planned on getting it, but I had happened to examine it earlier, and noticed that it had brand new sticks in it. Those alone were worth $150. So I bid $100, someone else bid $125, and then I got it for $150. I enjoyed that one for some time, and finally sold it for $300, just because it wasn't in living room condition like my other games (I sold EVERYTHING that wasn't in living room condition a while back).
Of course, there are also the things I missed. I lost a Roadblasters cockpit because I though the auctioneer was calling for $175, when he was actually calling for $75. So it sold for $50, and my predetermined ceiling on it had been $150 (had a video ram problem). I lost a Turbo cockpit to someone who just would not give up on it. I think he finally paid $275, and no one else bid except for me and him. Lost a Keno machine with a reset problem because I was slow in getting the $25 bid in (my stepfather REALLY wanted a Keno machine), someone else got the $25 bid in, and I wouldn't go $50 on it.