The demanding guest keeps you honest by telling you every time your attention wanders or your standards slip. Admittedly, demanding guests can drive you crazy sometimes. Your guests will always see things that you will never notice. Every complaint is an insight into how to make your business better. Every problem has a gift for you in its hands.
People go out to eat expecting to have a good time.
They want it to be great. Since you are in business to make sure that your guests are happy, the comments and suggestions they give are invaluable research into how to do your primary job better. This is where the gold is. Even if a complaint is entirely off the wall, there is still a nugget of truth in there somewhere. If you can dig it out, you can profit from it.