Some times the "cheap" aircraft on planecheck have damage history of unknown repair, some are widows-try-to-get-it-off-the-yard-sales-quick, some have few hours on an engine left, some half-started engine troubles ... whatever you can imagine, you'll find one.
Take one an engine due for OH and take two it is one of the small block old 6-bangers = we are talking up to 30k for the engine work in a decent shop, while the aircraft may be worth 25k after it. Instead of selling it along with a 5k gift, you go for asking 3k ...