New Member looking at a 2005 PreRunner

Good Morning from So Oregon. I have owned 14 Toyotas, currently a 2018 Highlander and a 2000 Runner with 5 speed and 235 K miles. Excellent condition. Recently offed my 2016 Tundra.
Did not need anything that large. I am looking at a 2005 Pre Runner. 140 K miles.
I know there is some consideration about rusted frames. I spoke with the owner (from 150 miles away) about this and he said very light surface rust and no flaking or perforation.
Based on that I drove the distance to check it out. Overall excellent plus condition.
Looked it over, spotless, never know it had 140 K Miles inside or outside.
Excellent condition overall. Well taken care of over its life. New rear springs, new Bilsteins all around, new $5100 transmission, new steering rack gators, $1700 worth of new tires etc. Inside unmolested, spotless. This vehicle is in Redding Calif. one of the hottest places in Calif and over 100 miles from the ocean and 30 miles from the closest lake. Very little rain. No salted roads.
I once again talked to him about rust so climbed under between the right rear wheel and the passenger door. Saw nothing. Everything else such as exhaust drive shaft and so on in excellent condition. Road test proved the vehicle far better than expected.
I put down a small deposit and would return with another driver so I could drive it home.
Meantime I am getting nervous based on a few youtube videos about rust. As I am going to pick up the truck this coming Tuesday I am thinking perhaps I did not give a more thorough look at the frame.
Dilemma, do I tell him ( 77 year old retired firefighter Forest Service Ranger) I want to look under the truck again but may face potential backlash with the appearance of insulting him because he is other wise a very straight shooter with 2 Lexus, newer Tundra, newer Tacoma, exquisitely restored and hot rodded 1975 Chevy truck..
I run a risk of offending him but do not want to make a very expensive mistake.
Any suggestions?

Thanks for reading, glad to be here.

 

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