I've recently adopted a rescue dog and have come across a lot of these issues myself. JoJo was abused by his previous owners and can be a little jumpy around strangers, particularly men, but he has never bitten anybody. Part of socializing him is exposing him to new places and people and have those situations be as non-threatening as possible. When people ask if they can pet my dog, I usually respond "I'm sorry, but JoJo isn't up to meeting anybody new. He was abused until recently, and strangers scare him." With that, people usually back off. Only once or twice have I had small children barrel up to him with parents behind encouraging them. In those situations, I put JoJo in a sit or down, stand between him and a child and say that he's being grumpy and wants to be left along today. A few parents have gotten huffy, but I say that I'm doing my best to teach my dog to be as well behaved as possible and for right now, that we haven't worked up to petting yet.
And for all you concerned E-Hellions, I don't assume I can drag him everywhere I go, I am teaching him to be well behaved, and when there's a stranger in the house, I crate him so he won't bother anybody.