That said, I wouldn't buy an old, low mileage diesel with dpf.
I thought 'old diesel' and 'DPF' don't go together - old diesels chuck out the smoke screen on acceleration because they haven't got a DPF. Newer diesels with a DPF are visibly cleaner in what they chuck out, and in the exhaust pipe because the DPF collects these otherwise visible deposits.
My experience of DPF's is purely down to the driving style of the user. Regular longer runs at reasonable speeds presents no problem as the DPF is burning off the deposits it collects. Low mileage pottering doesn't get the temperatures up to burn off the deposits, and that's when the problems start. But then you wouldn't buy a diesel and just use it to 'potter around', a petrol engine is the right engine for this type of use.
Another issue exists when users of diesels don't know the correct procedure when they get the first warning of a DPF issue - on VAG cars, an orange emissions light gives the first warning, and if the correct procedure (regeneration) is followed which basically involves a 15 minute run at higher engine speeds (motorway typically), the issue is normally rectified. If the normal driving style continues without remedying the issue, and the red warning appears, then it's a trip to the dealers. Generally, a simple regeneration procedure done using the computer is all it takes (its basically a programme that just automatically runs the engine through various rev ranges to clear the DPF)
Be aware on all those VAG cars of the A4/A6/Pisshat/Octavia sized cars, the front suspension wear sets in from about 80k. There's quite a lot of arms/linkages involved, and once one starts to wear, the others generally aren't far behind, and it becomes a never ending saga.
I also would have to disagree with the above. Part of my job involved driving a wide selection of Audi / VW vehicles, from new low mileage cars to older 'been to the moon and back' high mileage cars. Very rarely did I ever encounter suspension issues; the only main item that tended to wear more than others were the 'C' links (anti roll bar drop links), which gave a similar symptom to any other car when worn - a minor knock / clunk or rumble over uneven road surfaces. Ball joints, wishbones, suspension legs and coil springs and the like were very rarely an issue.
