The judgment that someone is a "jerk" for reacting emotionally to a boundary setting that thwarts their (perhaps unrealistic, but there you have it) hopes is an interesting reaction in itself.
Online it can be a short step from shopping to rejection (isn't consumerism all about the illusion of choice?). So I wouldn't be surprised if someone wrote a bad product review of me if I rejected the online product they offer--that is, their projected/constructed self.
If this is their way of reacting to rejection, and you find it frustrating, then it should be doubly comforting to you that you chose to reject them. To put it another way, they ARE "handling rejection," but it sounds like in a way other than you'd like to see them do. What did you expect?