[ThomasC]

Originally Posted by Lewismacfarlane

Amanda knew a member of the choir last night from another show

Of course she did.

A lot of the acts are already set up and then the judges act all surprised.

They've used people who are already known or in the industry. Obviously not all, but they do it quite a bit

The audience is fake as hell too and there's a huge amount of editing. They will be puppets and cheer/boo then that will be taken and put/used where they see fit. They are told how to react.