Great motors, but, as with any car, one or two things to look out for...

I changed by clutch, DMF and CS oil seal on my golf yesterday, and parts alone were £500 at a reduced cost: if it has a rattle on shut-down, or, and you may not get chance to hear this, a clunking/rattle on a cold (cold) start dip the clutch and keep it down - if the noise goes the DMF is probably worn/wearing out. It might only be a niggle, but its a potentially costly one.

Cam/followers - these can wear (long story short) if given the wrong oil/infrequent changes (my previous PD golf 150 had 3 cams incl the original by 110k - all before i owned it though) the whole top end might need a very costly rebuild at £1k +, so listen carefully for a 'ticking'/noisy top end. Ideally look/listen at a few tdi's before buying one so get used to the sound of a 'quiet one'.

Turbo's - 150's/130's run higher boost obviously, and a noisy/smokey turbo/car ... its all normal stuff to be honest!

Tom