My dad has a collection of customer-return string trimmers (cheaper ones, Ryobis, Homelites, etc) that he bought dirt-cheap. Most of them just needed fresh gas and some carb adjustments.
He also once bought a like-new Husqvarna push mower from Lowe's. It said it would barely run and smoked. He bought it dirt cheap because when he looked it over, he realized the previous idiot owner had filled it with oil...as in they filled it right to the top of the oil cap! Lmao.
Got it home, drained and refilled with the correct amount of oil, and it was perfect.