You seem to have that backwards, GMS are ALL like brand new, that's how I noticed it in the park to look them up and subsequently rent last week for 10 days. I've previously rented from Apple and BP and 'notice' the other scooters in the parks and THOSE are the ratty used looking scooters. In fact, if you see a preferred vendor scooter that looks new, it was probably bought from GMS as they sell off their scooters that reach 6 months old.
The only thing 'preferred' means is that those scooter companies pay Disney to let them leave their scooters at the baggage counter. In other words, they lack the customer service to provide a scooter directly to you forcing you to make the long walk to the baggage area to pick up and drop off each trip.
So, for the same price, GMS offers personal service, a Captain's chair (without asking), fan, cell phone mount and charging port, cup holder, unmatched reliability and customer service, and a free major accessory (awning or Oxygen mount or cane mount or back basket) if you wish.