I can put a muzzle and a 'don't touch' vest on one of our dogs and people still come over to pet her. "Oh, don't worry, I just love
dogs" they say as they're bending over her, reaching over her head, and staring directly into her eyes
So no, most times, I don't allow strangers to greet my dogs when we're out and about. On the rare occasion, if someone is standing still and looking right at me
while asking for permission, I explain the dogs are in training and I'd appreciate it if they could help out. I go on to explain the appropriate way to meet our dogs, hand them a couple of treats, and allow the greeting to progress. Some times we get lucky and the ppl are more than happy to participate by following the rules. Other times, if they go to make a wrong move, I walk backwards, and have our dogs follow by facing
me as I'm giving them a command ("look" followed by "let's go" in a happy tone). This way, I can quickly remove them from a negative experience while they are focused only on me and not the stranger.