I agree that there are often too many walk-throughs
and too much "teaching"
by the caller. At that point the most professional thing to do is to
apologize, choose a simple dance, and get people moving quickly to lively
music.
Just my two cents:
It has happened to me more than once that I've walked through a challenging dance,
feel it isn't clear enough, don't want to waste more time teaching it, and say
"let's do something else".
The crowd hollers "NO! We want to do THIS dance!"