Pro tip: stop trusting the $500 car guy who 'just did the timing belt'

I was at a gas station off I-35 in Waco last Saturday and watched a guy hand a kid the keys to a 2003 Corolla for $900 cash. The kid looked so happy, and the seller kept saying the timing belt and water pump were done just last spring. I said something to the kid after, asked if he saw receipts, and he said the guy seemed honest. Three days later that Corolla threw the belt on the highway and bent every valve in the head. I'm not saying every cheap seller lies, but a verbal promise on a $900 car is worth about nothing. If you're buying under 2 grand, ask for paper or knock the price down to cover the job yourself. Has anyone else watched a deal go bad right in front of them like that?