I've talked with hundreds of truck owners over the years, enough to have a pretty good feel for what they did and did not check out before they bought a used truck. They nearly all checked the electrical system to make sure that lights, the radio, the A/C and other features were working as they should. They took a look at fluids to determine if the levels were okay (and clean). Most everyone inspected the interior for rips and tears and the majority inspected a truck's important components -- like the brakes and tires. But there are a other system checks and pre-shopping tasks that are often overlooked, and they sometimes resulted in buyer's remorse -- a purchase the new owner later regretted.