NEVER ! ... All the booking agent cares about is the booking, and they make the musician/entertainer handle the situation ...
I used to get bookings through an agent and they were mostly good gigs, but once in a while he would mis-book me, like the time a yacht club wanted a young female to play and sing 'top forty' music, and he sent me - bald, stocky, at the time in my late 60's, primarily Standards/50s/60s player ... the audience liked the music for the most part, but I was not what they were looking for ...