I did one and it wasn't really as bad as you would think. But that would also depend on how cooperative the employees are.
Getting pictures of the four sides of the truck and the license plate was easy. I did them while they were inside cleaning.
Getting pictures of inside the truck depends on the employees allowing you to. Mine didn't have a problem and I don't think this was the first time they had been shopped. They didn't seem to really like it, but they didn't make it difficult.
I think they want to make sure you are upsold (stain resistance, pet stain removal etc), the employees are professional and that they use the correct cleaning solutions.
They pre-treat the carpet with one solution and then the buffer uses a solution as they go.
I'm not sure you could do more than one if you're in a small town like I am. Also, most of my house is wood flooring.