" You’ll soon find out some wizarding families are much better than others, Potter. You don’t want to go making friends with the wrong sort. I can help you there.”
He held out his hand to shake Harry’s, but Harry didn’t take it.
“I think I can tell who the wrong sort are for myself, thanks,” he said coolly. "

― J.K. Rowling , Harry Potter and the Sorcerer's Stone (Harry Potter, #1)