What you're probably looking at is a dealer "certified" pre-owned car. Volvo's flooded the market with them as they're all lease return cars, bought at auto auctions by the dealers used car managers and then gone over to become certified.

'99s are the #1 year S80 to avoid at all costs. The '00s are better but not nearly as good as the '02s on up. Some of the lease returns were maintained by their previous owners so if you're lucky, you might get a decent car. Do be aware of the fact that most who lease new cars have no intentions of keeping it past the lease SO they do almost no maintenance whatsoever which then might mean that if you get one of those, it's future is questionable IMO.

If you have ANY doubts, have the car inspected elsewhere before you sign the papers.