Check ebay too. Unfortunately now is a bad time to buy cars as they're more expensive and people are holding on to them more.
It's all about the servicing. Ideally you want full history. On cars of this age or miles see when the Cambelt and water pump were changed. Also check when the gearbox oil was changed. And if the car is quattro which I believe they are then the tyres should match with even wear on tyres on the same axle. Otherwise it can cause damage to the quattro system.
Also the headlights are bi-xenon and when the bulbs are going they'll go a bit dim or flicker. They've around £180 per bulb I believe.