Jessica’s Answer:

Because I can’t ask you why you’re turning down the work, if you want to work with this person, I’ll address this question based on two possibilities.  If it’s some other reason, put it in the comments section and I’ll answer based on your actual reason.
1. You are already working. In this case, be honest. Work is good. It means you’re “in demand.” Tell the person that you’d really like to work with them in the future. Then, offer one of your trusted contacts to fill the position. This way, when the next job comes up, if the person calls your trusted contact again, he/she can tell the person to offer you the job first.  If the person only wants your trusted contact, be happy.  Wouldn’t you rather you contact get the job than a stranger? And now that your contact is booked, if he/she gets a call for work, you will be recommended.

2. You don’t like the current job being offered. So, you don’t like what the person has to offer but still want to be considered for other jobs in the future. Tell the person you’re working and follow the steps of #1. If your integrity meter is flying off the charts right now because you think I’m telling you to lie, I’M NOT! Just because you’re not working on a show doesn’t mean you don’t have work to do on the business side. Trust me, there is always work to be done. My Greenlight Elites are working on “Busy Work vs Action” this month. They are in action each day of the month. They are working! 

If you have a question, put it in the comment section.
To your success!