I think, in general, most dog owners understand a bit of give-and-take with things like balls.
Honey never ever bothered anyone else's ball, until another owner decided that, as their dog wasn't interested in chasing their ball, they'd throw the ball for Honey instead - something clicked and she realised that ANY ball was fun, not just the ones we provided.
I can get a ball back from Honey, as long as the other owner can keep their dog away from Honey. In the situations where Honey has stolen a ball, I've generally found I have more control of Honey than the "victim" has of their dog... OH can't get a ball from Honey as easily, as he hasn't done as much of the training - but I NEED him to do occassional dog walks, as otherwise she just wouldn't always get a walk...
It took me a couple of years to be confident I could get a ball from Honey, and before that I carried 3 balls with me to swap/replace....
Don't give up!