170k on a properly maintained 4Runner means that it could very well have another 100k left on it. I'd suggest he have a mechanic look at the truck and probably most importantly, get a compression check before buying. I would also check out autotrader.com to see what trucks with similar mileage are going for in your area. I suspect that this asking price is about right.
Where in Beaufort are you? I'm from St. Helena Island, went to Beaufort High School (1990 grad) and my folks live on Lady's Island. Beautiful place.