U can usually get a good idea if the car has been well maintained within 5 mins of looking and driving it; scuff marks, scratches, poor conditioned alloys/tyres, lack of maintenace paperwork, damaged/missing items exterior/interior etc etc. I always get a HPI on it even from a dealer :-).
As for the cambelt, make sure its been replaced by VW dealer or respected VAG specialist backed up with receipts if the car is 4-5 yrs old regardless of mileage. If cambelt not done after 6yrs+ walk away! even if they say its been done but no proof, purely because its pretty certain the rest of the important servicing has been neglected. Paperwork tells the story of the car and how well its been looked after.
Yearly dealer/specialist servicing is a very good sign, however be aware some cars have the "long life" servicing with service stamps every 2 yrs, this is not what i personally like to see on a car myself, but if car is tidy then weigh up the pros and cons of this.
I myself steer away from modded cars or cars that have different oem specs like beige interiors
, research what is oem spec and list what expensive extras that are on it such as winter packs/ leather etc. High milers well maintained and clean are not necessarily the worst options as this could be motorway mileage and less wear and tear on clutch/brakes/engine, my car was ex-lease and has been no trouble at all for past 3yrs+.
Enjoy ur search and patience is a virtue