In addition to the well-taken point about rust and things that are disproportionally difficult/expensive to remedy, are there maintenance records indicating regular servicing? How does the oil on the dipstick look? Even if it is dark, it should not be thick. Automatic? How does the automatic tranny fluid look? It is bright red when fresh. Dark and black indicates neglected maintenance. Who did the maintenance? Are there wires hanging out under the dash or under the hood? How original is it? Even a neglected vehicle is easier to bring back than one that was "repaired" by a hack.

Other:

-What unusual noises does it make? Rattles? grinding? groaning?
-Can it pass your state's smog and/or safety inspection as is?
-Tires and batteries are cheap compared to other issues so that shouldn't be a major discouragement although factor that into the cost and your budget.
-There is a good supply of parts in junk yards.
-Volvo plastic, or any 24 yr old plastic is usually cracked or broken
-How mechanically inclined are you? What is your tool collection like.
-If all it needs is a tune up why didn't the seller do it and get more money or make it more marketable.
-It may be worth it to take it to mechanic familiar with Volvos to get it evaluated. AAA has a list of shops that are reputable, not necessarily Volvo specialists however. You will pay for an inspection.

That's a pretty open question. I would say first of all look for rust. You can usually tinker around with the motor and drive train of a 240 and get it back in shape. If there is rust though, you will be hard pressed to conquer it. As Neil Young said "Rust never sleeps."

These are other potential headaches-- at least for me):

trashed wiring harnesses
ripped, falling or non existent headliners
heater core or fan motor

The solutions to these problems are wildly disproportional to the effort, money, and attention they require.

Wiglaf