Regardless if you are friends or not, you can still buy from him. It's all business. If there has already been a falling out, and he is still willing to sell to you, then he still stands to benefit monetarily (albeit not much).

If you don't hang out, and he still will sell to you, that means there is still something in it for him. I mean, when you go to p/u, you can still be friendly without being friends.