As a salesperson, you are the "face" of the company. Customers don't really give a hoot about what goes on in a vehicle service area or a body shop filled with bondo dust. That's why there is a desk that separates you from those areas when you frequent them. Now- if the concierge at either counter was sucking on a PV while customers were walking in for service, your position would be an unfair standard. But your logic is apples and oranges when making your argument.
Good on your manager for sticking to his guns. I would probably be high-strung also if I had a team who blatantly disregarded my rules to the effect that you have. Especially feeling like he needs to take extra time out of his day to see if you are following the rules via security cam. I would be ashamed if my superiors had such a low level of trust in me.
Say why you will about his tactics, but I would thank him for being as lenient as he has been.