I have various experiences, doing demos:
One time, I came into a quite upmarket store (I'm still a student, and don't always get treated very well) I asked if I could listen to some speakers, the shopkeeper said I absolutely could, pointed me to his listening room . The listening room was upstairs and pretty remote, but he let me go about my business. I sat there for a long while, he brough me a cup of coffee, I listened some more and afterwards we had a nice talk about the various speakers. All in all, it was a very nice, unforcefull experience.
A different experience was a demo in quite a small shop, the store carries only a few brands, and it's quite small. I asked if I could listen to some stuff, and ofcourse I could. During my listening the shopkeeper sat next to me and talked throughout the music, making it hard for me to concentrate. Even though he was very kind, he did quite distract me. It was an odd experience, even though I was treated very well I find the whole experience anti-climatic.
These are just two experiences, but both felt extremely different. All in all, I can say I quite prefer to be left alone, though the salesmen should still show interest in my findings and help me in choosing a good piece of equipment.