My dog does this thing in which he only seems to really accept strangers if they throw his ball at least once. Food bribes are good for appeasing him, but if you really want him to trust you you have to throw the ball
So once I was cleaning my parrot's cage, so I put the upper part on the ground with the parrot in it(the cage is very sturdy and I was right there, there was no way my dog could have done anything), and my dog just approached the parrot and put his ball next to him and waited for him to throw it. D'awwww xD
Since that didn't happen, and because the parrot was such a shiny flying ball when he was out of his cage, my dog went on trying to catch him in mid flight and generally being jealous of him. But I never had much of a problem, really.