My Scared Miniature Pincher?

I have a 10 month old Miniature Pincher and he is VERY scared of strangers. He is so scared that if someone walks up and tries to pet him he pees and tries to be as far away from them as possible. This wouldn't be such a problem if people would just stop trying to pet him and get him to like them, it seems as if it is hard for people to accept that a cute dog like him won't let them pet him. Is there any way to get him to stop being so afraid?? He has always been like this since I first got him from Total Pet (a pet store in my town) and I am not sure why. After reading about Miniature Pinchers and reading how they are supposed to be so brave and what not, it is puzzling me as to why he is like this. The thing that I find the most puzzling is that he acts invincible when it comes to other dogs, no matter how big or mean they look he is not afraid. As with humans though he is petrified and it hurts me to see him this scared. Any tips or solutions???