Could be the belt but, it kind of sounds like the motor is stuck.
Easy repair in either case.
I would drop the appliance store like a rock. But, I would tell the owner, (very nicely), so they will know that you won’t be shopping there and that you will not be recomending them to anyone.
The biggest mistake people make is not saying anything to the owner. The owner can’t change thier ways if they don’t know.
Who knows, maybe the store will offer to fix it for free in order to keep you as a customer and a reference. (I would)
Good luck and Happy New Year,