Do a full VCDS scan, ask the dealer to test (this are standard test and anyone can request):
- full visual inspection test
- turbo test
- engine compression test
- check antifreeze and break fluid (it says something about the owner, if he was interested in doing a good maintenance or not!)
- check for brake disks (if you need to change them, it will add up some good $)
ASK dealer/independent to explain the errors if they exist, because usually they erase them!
(repeated lambda errors may show you need a new one, also expensive)
After purchase, do an oil change + all filters. Check the DV (prone to failure) and camfallower (also prone to big and disastrous failure) This are not to expensive!
Next step: Hit the gas and ENJOY!

cheers