With Auctions, I'm not talking about a small one with a few 100 cars. I'm talking big 1000 car sites that push volume ex-rental and lease cars. I know very little about cars, I've done oil changes, spark plugs and brake pads, bulb and batteries. I wouldn't have a clue visually if a car had a problems, I could probably see if it had been badly repaired but thats about all anyone can do. Just avoid the trade ins and we buyanycar bin sales.
Be very open about the type of car you want - i.e. estate, saloon etc, rather than bmw 325d etc.. and narrow your bid list down based on your research and visual look, then just watch the dealers bid. A £3K auction car will be up for 4-5k min in a dealers yard with nothing more than a coat of polish and a 3 month warranty. (which you could easily buy) You only have to bid £50-100 more than they are willing and you've got the same car you'd get on a forecourt.