Sluggo is right about that--- callbacks are the BEST! My daughter got her 4th annual callback to do one show, but unfortunately will not be able to make it this year.
He's also very right about your show needing to be "adaptable". In this annual show she does for a client she has to work with a group of 5 +/- year olds. She has to plan her portion of the show and then adapt it to work with anywhere from 5-15 girls (last year I think she had 16 girls) and she only has about 30 minutes (over the course of 3 days in 10 minute segments) to figure out how to use them. Sound easy? It's not! It is a lot of hard work and thinking on your feet. If she doesn't get it right, its her reputation. Somehow we always work it out.
You never know what a client will ask of you. There are some pretty out there requests-- and some while not impossible-- are not really part of your job so you have to measure what role you want to play in the party.
For example, we got one testimonial from a client who said my daughter was exceptional and carried the party (yada, yada, yada) but the only thing that would have been better was if she had served the cake. Well, that wasn't what she was hired for, nor was it ever discussed. I guess if they had wanted to pay her to slice and serve the cake at her rate-- she probably would have considered that too.

Although, that would have been a rather expensive on their part!
The bottom line is that you will never know what a client may request from you or how you will have to adapt yourself and your show. Again, the more prepared you are, the better you will be able to adapt yourself to your client's needs.
Happy preparing Lierke!