How wedding entertainers handle guest requests
Guest requests get treated as a problem to be managed. Handled properly, they are the best live information available about what the room wants.
The default position should be yes. Somebody walking up to ask for a song is telling you they want to dance, which is the entire objective. A request that fits the night and fits your do-not-play list is a gift.
The exceptions are real, and they are yours to set. Anything on your do-not-play list is a no, always, regardless of who asks or how insistent they are. That is not the entertainer being difficult. That is the entertainer doing the job you hired them for. Your list is the boundary and it does not move because a guest is persistent.
The judgement calls are about timing, not taste. A song that will empty a floor at 9pm might be perfect at 11:30. Part of the skill is holding a request rather than refusing it, and knowing when it becomes right.
How to set this up in advance. Decide whether you want requests taken at all. Some couples want an open floor, some want everything routed through them, some want it left to the entertainer. All three work. What does not work is leaving it undecided, because then the decision gets made at the moment somebody asks, by someone guessing what you would have wanted.
Give your do-not-play list honestly and completely. It is more useful than your favourites list, and it is the one thing nobody can work out on their own.