Check the oil dipstick and make sure it is clean, front axle shafts are common, find out the mileage and inquire about the timing belt service. If it has been done ask for receipts. Also the retarded front suspension always has something loose in it mainly one of the 4 control arm links, 2 on top 2 on the bottom. Ask about transmission issues if it is an automatic. See if the check engine light is on, if it is not at least when you turn the key on to make sure the bulb actually works.
Otherwise they have a lot of little issues with the air injection system and vacuum system both of which usually sets codes. The 1.8T also is known for ignition coils going bad usually one at a time. If the mileage is up near 100K look at the flex pipe and see if it is coming apart if it is starting too be ready for $1300 for the flex pipe and catalyst they are one piece that bolt to the back of the turbo.
If it has more than say 75K I would seriously pass.