All i'm saying if your characters have a believable history the dialogue will be believable just like real people. I think it's a bad mistake to listen to conversations from strangers and working it in the dialogue. Every person is different you see. So are your characters.
Surely backstory helps you work out WHAT your characters will say.
Dialogue is about HOW they say it. I like that to sound like real people. So I like to listen to real people.
Anyway, we all work differently I guess.