I wasn't criticising your role (or any that of other mods/admins), merely pointing out that here at least you have control over that sort of thing, so you wouldn't have to put up with it if it was that big a deal.
As far as retail experience goes, I worked in retail for many years before going to uni and doing various degrees and research over the following decade to escape it, only to pop out the other side and start a business manufacturing and retailing products/services. I don't claim to be any sort of sales expert, but I have my fair share of experience dealing with customer needs, desires, and complaints, both logical and irrational. Can customers be unreasonable and petulant? Absolutely. Is it justified? Sometimes, but mostly not. Does that make a lick of difference either way? Not if you want to stay in business. Dealing with unreasonable demands is part and parcel of retail sales/service.