When I was in college, the orchestra director gave the ensemble a new reason for performing better during a hit-and-miss rehearsal.
"There's talk of charging admission to our (previously free) concerts," he told the orchestra. "Would you pay admission to hear that?!"
I thought but didn't say, "Probably not, but the concert is almost a month away. By that time, everyone will undoubtedly have their music down. This is a rehearsal. Musicians make mistakes at rehearsals that they won't make in concert, once they've practiced their music frequently and played it at enough rehearsals."
The concert turned out well, as I figured it would, and the audience got its money's worth. As far as I know, no one asked for a refund.
