I know some people believe in using a whole lot of treats, but our trainer said it is not a good idea to let other people feed your dog.
That is true.
Because the dog will go over threshold for something rewarding, and if he's approaching someone for a treat and going over threshold but the person doesn't have a treat then you could be in trouble.
My boy isn't fond of strangers and it worried me about his CGC. I started rewarding him for allowing people to put him or going up to people. So he could go up on his own time, treats are coming from me, and I can watch his theshold myself.
So he goes up to sniff someone "yes!", treat, allows someone to pet him "Yes!", etc. And he did earn his CGC.
But definitely manage situations, learn what makes him more uneasy. For my boy it's when people immediately fixate on him and approach. If they approach and ignore him he's much more comfortable with them. Turning to the side also helps.
Also he's better in situations where the people were already there, rather than going somewhere then they approach.
Hopefully this isn't too jumbled and makes sense.