Not sure what kind of scoot you have but my stock tire feel out of balance to me I've only had it for about 3 weeks dealer ride it and said it felt fine to him. Did you have the same experience with your stock tires?
That dealer rides all sorts of "crap" scooters daily. He has nothing to compare to except the bouncy/bent/out of round crap that is everywhere in the scooter business.
I'd make them balance/re balance the tire. No excuses there at all. You know your bike He doesn't. If he holds firm on being a dick try Dyna beads or Ride On TBF (Tire Balance Fluid)
For all the rest of the posts... YES tire pressure is Very subjective, and personal. Like a Mattress at home. Everyone has a certain feel they like. Two or three pounds can make an unsafe bike safe or a safe bike unsafe.
Find an air source that you can sort of "test ride" around. Experiment. It's the only way to find your "magic number".