I wouldn't buy ANY car with that problem. But if the seller put 4 new tires on it and the vibration was gone, I'd have no fear. Tire problems happen on both 2WD and AWD cars. The difference is as Frank mentions - you need to replace all 4 tires at the same time on AWD.

If you had one bad tire on a 2WD it might cost $90 to replace. To replace the other 3 on an AWD it might cost you an additional $270. I'd be willing to spend that much extra every year for AWD. I now drive an XC that saves me around $75 a month in fuel compared to my previous SUV. It's more comfortable and handles much better although I occasionally miss the interior space.