I bought a 1998 V70 AWD w/ 99k miles on it. Some things I noted when I researched it:

- 1998 doesn't have that messy computer problem introduced in the 1999's (search the board for posts about it, there are plenty about)
- low pressure turbo (non-T5s) are less likely to fail than the high pressure T5 turbo; I didn't look at T5 cars for this reason
- AWD can go wrong but didn't see many posts about this and my mechanic (Volvo only mechanic) hasn't seen any issues so issues are likely smaller percentage
- check to make sure all recalls were performed; Volvo issued an airbag recall (found it in the carfax report) on a missing ground wire for the airbags which caused them to randomly go off; seems kinda important

That's all off the top of my head. Good luck!