No, don't want to work in that industry

This isn't always necessary. You can just say you're booked (see

No, I don't want to).

Hey!

Thanks so much for the email.

Unfortunately, I’ll have to pass on this project. I’m currently booked, and don't take on jobs in the ______ industry for personal reasons.

Best of luck! [If you’re looking for designers, I can recommend...]

Cheers