Re: 1999 Regal Commodore 258?
Look for signs of water leaking into the cabin. Stains in the headliner or carpet are obvious, and water rings in any cabin compartments would be another sure sign. The hull/deck joint on those is held together with screws at the rub rail and they are installed with no sealant of any kind. After a few years and flexing from waves, water can easily penetrate the screw holes even with the screws filling them. It's not a tough thing to fix, and it's certainly not a problem limited to just Regal, but it's a good way to get the price down. Good luck.
If you like Regal boats, you might prefer the 1998 through 200? 2550LSC model for weekending with a small family. It's a big cuddy that sleeps 4 and has less cabin and more cockpit than the 258. It's also lighter, faster and sleeker.