Batteries. Ask the seller to charge the batteries over night before meeting. Check that the power gauge is at full, both before and after test driving - a large drop in power after test driving indicates poor batteries.

Testing. Give the scooter a test drive for at least ten minutes, make sure all is working properly, if possible go up and down hill, make sure it drives safely and consistently, and that it is properly adjustable and comfortable.

Rusting. Check around the scooter especially the motor and steering areas etc for excessive rusting. Many intermittent problems are caused due to a scooter having been left in a damp environment for a long time.