I was in a Comcast office trying to trade in a set-top box for a CableCard (which is a whole separate pile of bullshit by itself). As you might expect, this inevitably resulted in the rent-a-deputy (not just a security guard, but a damn officer of the state!) that Comcast had hired to deal with irate customers (i.e. all of them) taking notice of the situation. First he told me to leave for "disturbing the peace." Then, he followed me out the door and stopped me, which is when I asked "am I being detained?" After waffling on the question, he told me to go back in the store and deal with the customer service rep because otherwise they wouldn't count the set-top-box I'd put on the counter as "returned" and keep charging me for it (as if Comcast's incompetence is his problem).
I almost should have suggested that if Comcast did fail to log the return then I could just cite him as a witness to prove it and then left anyway, but -- like I said -- I genuinely wasn't sure if he would have arrested me if I tried.