Ok, so here’s how I look over stuff (this is kinda my job). Get inside, start it, make sure everything works like it should, radio, heat, A/C (if equipped), seats adjust, windows work, etc. Check for an owners manual and such. Pop the hood when you get out. Open the hood, check for turned bolts, damage to the radiator support and inner fenders. Core/radiator supports like to rot out down by the frame rails and being that they are welded in, it’s usually pretty obvious if it’s been replaced. Turned bolts (the factory paint is chewed up) doesn’t always mean it’s been replaced or repaired but will tell you if you need a closer look. Feel around the edges of body panels for a tape line. Look down the body lines and see if it’s straight. Look for flat paint, excessive dirt in the paint, runs and “fish eyes” as more indicators of something being painted. Check the rear leaf spring hangers shackles and the frame around there for bad rust. Check the frame up by the front of the bed on both sides where it curves down towards the front of the truck, frames like to rot there. On the passenger side, check the crossmember right behind the cab and the next one back for rot, usually by the frame.
Carfax is worth less than the paper it’s written on. I’ve seen totaled vehicles that have “clean Carfax, one owner” and such. Not sure how flippers do that, but they do. I do know that Carfax only reports what is out there so if you wreck your car and don’t go through insurance to fix it, Carfax doesn’t have a report. Rust holes in the frame are technically classed as frame damage and although often repairable, kill the value. Repaired frames still class as frame damage, but it’s acceptable if it’s done right. FYI, since the inner fenders and core support are welded together, any alterations or damage there also class as… frame damage. Also usually repairable and done right is considered acceptable.