If you need to hire a tech to inspect your purchases should you even be in this hobby? To participate in this hobby you need to have enough technical knowledge to do a pre-purchase inspection yourself (and know when to walk away). Otherwise just purchase a new Stern or buy from a local dealer who will warranty and come out to fix as needed.
As to the original topic, always test a machine running before buying.
Sounds like both participants in this deal dodged a bullet.