The Volvo is going to be a no go.
Yesterday morning was on the cool side, so I took the Volvo for a quick run to see if the colder weather made a difference. I also asked Evelin to watch me drive away to see if there was any smoking. It didn't give out the big puff of blue-gray smoke that the Mazda used to, but it did have a small, continuous plume of blue-gray/white smoke, which makes me think it's burning more oil than I'd like for it to.
That wouldn't be ideal, but the seller said that it sometimes took a quart of oil between oil changes; I could live with that. However, this morning, I had Evelin drive it so I could observe the plume. When she stopped at the top of the hill, however, I noticed the brake lights weren't working. After a bit of experimenting, it seemed that it wasn't a fluke: The brakes were nice and tight, but the lights didn't go on.
Maybe this was weather related (it rained overnight), but brake lights are something we'd like in a car. Plus, Evelin's uncle had said that if the rear lights weren't working, it could be expensive to repair, and we'd have to repair them for the inspection before we could register the car. The other lights all worked, however, which was a little odd.
So that's that; we're not having the mechanic look at the car, and will return it to the owner tonight. And then it's back to CarMax, eBay, etc.