A friend of mine drove an old Mercedes till the wheels almost fell off and when she upgraded she bought a used Land Rover LR3 from up north. I asked her if she had ever even considered looking underneath it. The frame and suspension was absolutely ruined. I think she kept it about 6 months or so.It's amazing how often people fail to check out the underside of the vehicle they are buying. It's common for people to haul rotted vehicles down from the north to sell to folks that never had rust issues like the salty roads up north create.
I found one example when I went to check out a clean looking with a decent price '05 F150 sometime in 2014. Took a peek underneath and found that the frame had spots that could be poked out with a screwdriver, someone had thought black paint would cover it up. Told the salesman & he gave me the response that it was "treated" and is good to go. Last time I ever went to that dealer.