if its an auto ...check the box, then re check it, then find out when (if...) the fluid was changed, then pull a sample of the fluid and check if its burnt...

volvo do a sort of fluid for life line on these boxes, but also say ifthe cars heavily used (aka taxi) change every 35k...most people in the know change every 30k anyway..did mine at 60k (suspect original fluid as it had full volvo service history) and was VERY glad i did...

other than that check for oil leaks between the engine and box...leaks = blown rear seal...say hello to an expensive job, but bear in mind my indy mechanic says they ALL go in time (he says somewhere from 30k t0 150k no rhyme or reason when...)so unless its been done if i did find a leak i would use it to negotiate...on the basis of i would probably need to do it some time...

the uper engien mount will be shot (look for a tear in the central beam) easy fix (like $20 and 20 minutes and some ingenuity) - unless its been done, again a good negotiating point...

check the air con, if the core in the dash is leaking its BIG money - and not easy DIY...

but its rather like a 740...they have their week points but IMHO the 850/v70 is a good car..(and i have a 940 too, which by comparision is more grief..but higher milage and builti n belgium rather than sweden...)