Explain what you are doing and why; if they don't want to let you try it, then you aren't interested in buying it. It's understandable that, out of ignorance,

Explain what you are doing and why; if they don't want to let you try it, then you aren't interested in buying it. It's understandable that, out of ignorance, they aren't comfortable letting you do that... it's equally understandable that you wouldn't pay thousands of dollars for something you can't even play with for a few minutes in the store first.