it's usually indicative of a camber problem which happens a lot when either the stock suspension is worn out, or the vehicle has aftermarket springs. many aftermarket springs will have a .8 inch drop which makes the top of the wheels pull inside and the bottem push out. My Z does this because the stock shocks/springs are worn out and need to be replaced and the negative camber is easy to see with the naked eye. I would think the car would have to be driven pretty hard to kill the stock springs/shocks in 50k miles but it is also really old mine were wore out when I bought my 90' with 98k. If it is because of aftermarket springs it is easily remedied with a 300 Degree camber correction kit or with udjustable upper A-arms depending on how much you would like to spend. I definately wouldn't drive the car 400 miles with the tires worn that bad. at the very least by some cheapo used tires to get home, and you have the suspension checked at the same time.
A couple years ago 13.8k woulda been a good price for a car like that but things have turned down a bit so I would try to negotiate on the price a bit more.low miles are nice but if your questionable about the condition I would try to get it down to 11-12k which I think is reasonable. try searching classies here to see what some similar milage cars have gone for recently.