It was somewhere in between they were nice about it and they felt that they deserved it, if that makes sense.
It does. Most people tend to behave nicely as long as they still think they're going to get their own way.
In situations like that it's not impolite to ask: "How long is it going to take?"
If the answer you receive isn't reasonable (say ten or fifteen minutes) or politely given, you're perfectly within your own rights to remember that you too are a customer of the store and simply but politely decline - or suggest they resume their video shoot after you've finished.
I'm guessing the store would feel the same way about it.

