You have to apply to be in the audience and the applications asks you to give examples of questions you would ask in relation to certain things. I guess they pick the most suitable candidates from the application forms.
Its always been like that you have to submit your questions first as well for that reason I have stopped watching it to me its vetted too much if they had to answer off the cuff maybe it would be worth watching
It came from Barking last night - My Dad lives in Barking - wasn't sure where they got the majority of the audience from, but it definately wasn't Barking. hahaha
I have appeared on QT, and as advised, you have to apply, and are selected.
Years ago, they always advised that the audience were selected as 'representative' - but I don't think they say so now, although the format remains unchanged.