I have had it happen a couple times during doubles rounds. I would throw and turn around and see one of the other guys looking in my bag. But that doesn't bother me too much, because it had been early in the round and i have some idea of who the guys were.
But a random stranger when its just me on the course needs to ask for permission before they dive in. I don't have any fancy stuff really. I mean a few Lat 64 discs, occasionally some MVP, some limited run wizards, and then metal flake and what not. So some of that catches peoples eye and they get curious, but still ask I will gladly show you and tell you what they are.