Single post in Questions about Site Rules
That is a good question, the only thing I could find was in the gym subforum in the battle forum. "Please note that any fee for a Gym on top of the one for setting up a battle in the Dojo is not permitted. This includes fees to battle and fees if you lose to the Gym. However, you are welcome to reward the victorious challengers." But if it's just individual challenges it doesn't really say anything. Actually it doesn't look like there are any individual rules other than bump rules in the battle area, and only in the gym area. So hopefully a mod can shed some light on this. And if these rules do apply to regular battles, perhaps there needs to be some clarification on the main battle forum.