Duh, of course salespeople are human! That "shell" you refer to has a lot of purposes. One, it lets harsh people who give them crap bounce off of them. Two, it lets them kind of zone out until they can clock out because I doubt most casino workers want to be doing what they're doing -- they're just doing it to make ends meet. I certainly wouldn't want to face the overall implications of running around a dark, smoke-filled room in fishnets and high heels getting gamblers drunk so they can ogle them. Or fishing for tourists with timeshares and free show tickets.
I hope that I don't forget that when I've moved farther away from my high school and college self, working retail to fund my independence until I had the experience/education necessary to move on.
Despite the overall tone of this post, though, I must say that my experience working in retail was overwhelmingly positive. The vast majority of customers out there aren't out to get you, and many do take the time to connect with you as a human being, whether they're a regular or not. The only bad retail experiences I ever had were because of coworkers, not customers. Even my more recent dabbling in commission sales hasn't been all that bad. People are wary, yes, but not mean (unless they've got other issues going on), and some people are downright enthusiastic.