Is this the truck you're considering?
https://portland.craigslist.org/yam/...065736206.html

If so, it does look good as much as the single photo can reveal, but with 250k the asking price seems high, especially if it needs tires. As geezer101 stated ask for receipts of prior work. With that many miles I'd expect it's had significant engine repairs as well as trans, brake and possibly suspension work. Receipts will support the sellers price, but in their absence, a lower offer is appropriate. Consider the near-term costs (tires, title and license transfer) first, then take a guess at more long term, potential costs and repairs based on the truck's documented service history to arrive at an offer you can afford and consider fair.
As to the bed rust potential, look underneath around the drain holes at the front corners of the bed. Also inspect the tailgate hinges for rust. Their condition might provide warning clues.
Also, in case you didn't see it, there was a Gen2 4wd long bed on CL in Vancouver, WA. Body was rougher and the seller didn't state year or mileage. But he claimed to have rebuilt the engine. The ad is now gone and he was asking 1850 or best offer.
Good luck.