As it's not your usual car dealership, it's not just a car - the impact would be far greater if someone decides to plow into a group of people at Pillbox in an aircraft.
Being able to sell them requires being in staff, as we're trusted to sell them to people we think may
NOT cause issues, and follow procedures to train people before we allow them to purchase one etc.
There's a lot more to it, but I'd suggest finding out in RP.
As for not being able to find someone working there, you may just be not asking the right people - or not around at the same time someone's there.