Triple check your towing by contacting Buick with your VIN#....before you sign on the dotted line.
On the price, IMHO it's high. We just sold our immaculate Rockwood ROO 23SS for $9500 with a ton of extras....Equalizer hitch with sway, brand new tires with only about 1500 miles on them, Adco winter cover, outdoor rug, linens for both beds for summer and winter, propane grill that attached to the exterior, PopUp Gizmos, and a bunch of extras I can't even remember. I'm not totally familiar with the model you're looking at, so can't compare that, but ours had been stored undercover since shortly after Day #1 and if you set it next to a brand new one, you'd be hard pressed to tell the difference. Others that are more familiar with that model can probably offer better advice, but I would think in the $6000 - $7000 bracket if it's in near perfect condition would be reasonable. Suggest you do plenty of homework on both your tow vehicle and comps on that camper. If you haven't run the NADA numbers, suggest you do that. Enter only the year, make and model WITHOUT any extras like A/C or awning. Those don't really count with NADA. That should give you a good ballpark. Good luck.
