63,000 miles? 163,000 miles? 263,000 miles? Unfortunately, you can't tell how many times that particular odometer has turned over.
Maybe for that price it's really not important to you, maybe it is.
Let's see. 2016 - 1988 = 28 years old. 63,000 / 28 = 2,250 miles a year, on average.
Let's say the odometer has turned over a time or two.
Maybe the current owner hasn't owned it too long, and he genuinely believes it only has 63,000 miles on it. Or maybe he knows and is lying about it. If he's lying about that, what else is he lying about?
If you're really interested in it, I'd get the vin # and buy a CarFax. The history part will tell you how many times it changed hands, and what mileage was reported to the DMV each time.
Oh, and see if there's an hour meter on that Onan Generator. Might be real interesting to see how many hours are on it.