Its a lottery buying a car from the auctions. I had a cracking bargain on an E39 because it had a rattly cat. I knew this however as my brother is a driver for them, so gets to test them out
People thought it was the big end bearings.
Go to a local one and don't be afraid to chat to the drivers, most of the time, they are happy to chat to anyone.
What you have to remember is that the hammer price isn't the price you end up paying. Normally, you have to pay buyers premium, which could be anything depending on the auction, but factor in 10% as a good rule of thumb, then add on VAT onto that. If you pay by credit card, then its another 2.5%
I've been through auctions with cars at over 350K miles (Nissans) which drove flawlessly and 58 plate Corsa that had been ragged to within an inch of its life. What you have to remember is that auction stock comes from a number of places such as:
Cars too old for dealer stock (maybe a full service history, but age prevents it being on a forecourt)
Private - People who can't be bothered advertising it
Private - People wanting to get rid of a lemon
Trade - People wanting to get rid of a Lemon
DVLA - They don't care as long as it makes a little bit of money
People also very at these places. Some auctions are pretty good, others I have seen take bids off the wall or have people who join in on bidding without the intention of buying (Shills) These people are only there to get the price you pay up and are sometimes employed unofficially by the less scrupulous auctions.
Get there early and have a good poke/prod and always take a magnet/print out of what price the car you want/definite ceiling you are willing to spend.