Sam, age 13 or so, seeing the hickeys on his brother's neck, feeling sick with worry and anger and jealousy and guilt, and he can't bear anymore to see that and to know what happens and to imagine all sorts of images, goes to Dean and begs him to stop doing what he's doing. He tells Dean he knows what's going on, how Dean is getting the money, and that it's not worth to go and do that so they can have food when Dad's not around...
What Sam doesn't know is that those hickeys are actually from John - Dean wouldn't let strangers mark him up like that, no matter how much they're paying.
