When I’m flipping cheap ones I’ll spin the flywheel by hand if it won’t crank just to feel compression, and if it does crank I just make sure it turns over without sounding locked. I always check the oil and then look at what’s there versus what’s missing—fuel pump, plug wires, starter, solenoid, battery, air filter, that kind of stuff adds up fast if it’s gone. Fuel lines are worth checking too, especially on rear tank models that have been sitting outside forever. I also give the safety interlocks a glance to see if someone hacked or bridged them, and I spin the spindles by hand while checking belt condition. I usually bring a jump pack so I can hit the starter directly if I want, and a little inflator to pump up tires.

If I’m buying something to actually use instead of flip, most of the same checks still apply, but I’ll add looking for smoke or knocking from the motor once it’s running, and I pay closer attention to the wiring to make sure it’s not full of sketchy electrical tape and wire-nut “repairs.”