My horse is an evil hound with treats. She gets to excited and uses her teeth to grab em. We had two people who always came in and gave horses treats and that just made Gypsy worse. I just put a note on the small white board thing that was on her stall. It was in red ink but asked nicely not to give treats. It works if you can't actually catch the person in the act to explain why.
Glad things worked out with the manager
From east to west a travlin gypsy found her prancing pony for now their hearts run as one...into the north