You haven't metioned how many miles it has or how many previous owners.
I personally wouldn't look at it unless it comes with a genuine, fully documented, service history. That is the starting point.
If it has been well maintained then the log book should give you a good idea of what and when everything has been done and also what probably needs doing in the near future.
Failing that, the timing belt age/mileage is critical because if it lets go, it will probably destroy the engine.
Check for crankcase pressure, oil leaks (especially around the rear crakcase seal) as this is an expensive repair job.
Also the A/C is known to have problems - run it through it's paces to see if it cools the cabin area adequately as Volvo A/Cs are also very expensive to repair.
Suspension and brakes need to be thoroughly checked over as they tend to go through rotors fairly quickly.
A crook Volvo can turn out to be an expensive pain-in-the-a$$, but if you happen to buy a good one, they are very reliable, roomy, comfortable and a really delightful vehicle to own, and you will soon find yourself loving it to death.