Be suspicious of neglect...

Whilst under the car, check the exhaust for corrosion. Look for corrosion and welding repairs to structural and load bearing sections. If you find extensive rust, or any sign of fibreglass or body filler in these sections, reject the car. If the car shows evidence of neglect, like dull and faded paintwork, missing trim, cracked windows, lights and mirrors and has a generally dirty appearance, you should always be suspicious. Wear to the mechanics will probably have been accelerated by a lack of routine maintenance; all manner of problems could await the unwary purchaser.

At a lot of auctions the cars will be unlocked and you'll be able to have a good look inside and under the bonnet. First, open and close the doors, tailgate and bonnet to make sure they fit and operate properly and that the gaps between them and the bodyshell is equal all round. Look of the upholstery, trim, headlining and carpets for signs of damage and wear. Does this and the wear to the pedal rubbers tally with what's on the mileometer. If the Speedo says 40,000 miles but the driver's seat is threadbare and sagging and the pedal rubbers are worn down to the metal, there's something wrong. Brand new is as bad as worn through.