I’ve had that very thing happen on several occasions, and I’ve handled it with a command voice advising “stop; don’t come any closer,” that they’ll get no $$ from me, and “you need to move along!”
Only once have I needed to move my hand to 3:00 on the outside of my shirt; which caused an instant retreat. I didn't brandish any weapons, or place my hand directly on my carry gun.
I won’t let anyone get too close (still farther away that six feet), and I’ll maintain distance from them, even if I have to play “circle the truck.”
I won’t unlock the doors if anyone is in proximity, and only unlock the drivers door when I do. I don’t have it set to unlock all the doors on entry (unless I press the fob button a second time in quick succession).