Yep, usually buy all my families cars from the auctions. Just bought a nissan note from BCA Manchester two weeks ago. 07 plate, 19000 miles warranted, fsh and fresh MOT, for £3500.
It can be a bit overwhelming, but there is some good deals to be had.
My tips are:
Get a price guide and look at all the cars your interested in, also go to the network q website, they have a value your car link that takes you to Glasses website, almost every dealer uses Glasses guide.
Get to the Auction early, get a program and go and look at the cars that you are interested in, check out everything on the bodywork, work your way around the car checking paint and panel alignment. Be there when the guys unlock them and check out the interior for wear etc, be there when they start it up and look for any warning lights on the dash, also listen to how it sounds on start and if there is excessive smoke from the exhaust.
If its BCA that you are going to they will have a print out on the windscreen, check if mileage is warranted and MOT/Tax etc all this should be on the print out.
Listen to what the auctioneer says about the car when it is driven into the auction hall, and have a price in mind (I usually use the bottom book price + £200), remember there will be a buyers premium to pay on the bid price so factor this in. Always stick to your price limit, that is important, your there to get a good deal not get in a bidding war with another buyer, there will be other cars.
Also, try to get one of the ex lease cars rather than a main dealers PX. You will also notice that the prices go cheaper later in the day, as most dealers will usually go when they have bought their quota.
Always aim to get it for at least £1500 less than what the main dealers are selling it for.