There are quite a few similarities between the two scenes. Both brothers are determined, demanding that the demon (always a bit slow to appear) "Come on". Both demons reference how the brother they are facing is following in the family tradition (“Following in Daddy's footsteps. You wanna make a deal.” “You want to make a deal. And 'round and 'round the Winchesters go.”).
But there are differences, too. When faced with the demon, Dean threatens her ("I should send you straight back to hell."), and only admits what he wants after she calls him on it. Dean then offers his deal (reminding the demon his soul is valuable: "There are a hundred other demons who'd love to get their hands on it."): Sam back from the dead, and ten years for him. When the demon turns him down, he tries to bargain. The crossroad demon calls him on his bluff.
Sam, as he tells the demon, isn't playing games. While Dean tried to bargain, Sam explicitly asks for nothing. "I don't want ten years. I don't want one year. I don't want candy! I want to trade places with Dean." Dean faked not being desperate, and failed. Sam doesn't bother faking. While Dean tried to play up the value of the soul, Sam just says his offer is "a fair trade".
By the end of Dean's negotiation, she has complete control. "It's a fire sale, and everything must go." She agrees to bring back Sam with more than little condescension ("You're like a... puppy. You're just too fun to play with."), and throws in one year for Dean because she is a "saint". It's as much a humiliation as a favor.
Sam, who is open about his desperation to point of aggression, ends his negotiation by killing the demon (or at least, so is implied). But though his opening offer was lower than Dean's final agreement, but he doesn't get Dean back. Sam didn't bring any false pride to the table, and as such can't be humiliated. He asked for nothing, almost demanded it, so nothing he can or can't get could bring him down a notch. But Dean ultimately got a deal, and Sam did not.