Check the rear door seals, they love to go. Symptoms are damp rear carpets (if the passenger side has it then be aware the entire loom goes under that side and if it's been left for a while then it will rot it and a loom is a large job on the car). There is a fix involving removing the doorcard + sealant - ask if this has been done or crack out a bucket of water to check (inside will mist)
Other common things are the blade that controls recirc / temp, check it blows a varying amount of temperatures through the cabin. Brake light switch goes, there's a better replacement version, they cost bobbins if it happens.
I ran through 2 examples to 130k+ 4 years ago, i lost one turbo in one (£600), the other suffered a front engine wiring issue (£200) + brake switch, both suffered from the water issue. Used an indie to service both, fairly cheap costs and consumables (tyres are 16" so fairly cheap). They are getting on a bit now but if it's got the history then it will be fine. I sold both to uptrade, both were in excellent nick at 130. No DPF, you get to smoke everyone out if you hammer it to the tune of the tdi clatter