As mentioned, a build up of engine sludge due to longlife servicing and the use of the wrong type of oils is the main issue with 1.8T's. "If" you buy it it's well worth you dropping the sump, and cleaning/replacing the oil pick up as plenty of engines have died through oil starvation with this. Then you'll know you've a good car which will last and last with the regular quality oil changes.
Otherwise, check the coil pack and plenum chamber gromet recall has been done. Other issues are:
1. Makes sure all doors lock/speakers work, wires break at the hinge point.
2. Check the glovebox lid.
3. Make sure the wipers aren't 'slow'.
4. Aircon works and as you direct the flow it comes out of all selected vents.
5. Make sure the engine undertray isn't missing or hung off.
I'm sure there's more, none of the above should put you off, but forewarned is forearmed
