All the time, but it usually doesn't manifest itself in a direct rebate. Instead, they will go out of their way to double check something, point out a better option, or letting me know of something completely unrelated before word gets out to the masses.
Just two weeks ago I had to get a medical exam done for immigration purposes. For the uninitiated, everything that has to do with immigration is bloody miserable. People are in a terrible mood from being jerked around by the paperwork, lines are awful, etc. It makes a trip to the DMV look like a walk in the park. When I get to the little clinic, the desk staff is overwhelmed, and being treated like shit by everyone in the waiting room. They have people who don't understand English too well (which isn't their fault, but it doesn't help), which makes everything so much slower and pisses everyone off even more.
So when it's my turn, I not only have all the forms already filled out and my payment card in hand (unlike the previous dudes who had to scrounge for money for a good 5 minutes), I also apologize for having medical records in 4 different languages and tell them I don't know much about shots but to just let me know if I can help translate in any way. At some point, they ask me whether I've had a specific shot, and I have no clue, if they can't find the record I guess I never received it. They can't find that particular shot record so they decide to add it to the bill and tell me to wait some more until a nurse can administer it. 10 minutes later, the front desk lady informs me that it's not necessary, she had gone out of her way to look up every line of barely readable doctor handwriting into some international database and it turned out that I had indeed received the shot, saving me a cool $60.
Not too bad for smiling a little and bringing a book instead of moaning.