When I created my first video demo tape I taped four testimonials immediately after the show. Here's how I set t up:
Before the show I did a little strolling magic, meeting people and screening them for the testimonials. After entertaining with a few close-up tricks, I asked them if they would be willing to make a few comments after the show for the videotape. All agreed.
Immediately after the show, the camera person and I went into the hotel lobby and did a quick interview. I stood off camera and asked them to say how they liked the show, what they liked in particular etc. I got four terrific testimonials and I will do it again, if and when I redo my tape!