If it makes you feel better, I certainly am "screaming in opposition" about this. But I'm screaming at Horo, not Lawrence. She sold herself, and she knows it.
If Lawrence had just said "Sure! I'll sell Horo!" then he'd be a total rat bastard and we'd all want to hang, draw and quarter him. But he *knows* it's fundamentally wrong, and doesn't want to do it, even when she gets upset at him for pointing that fact out repeatedly. In fact, he's looking for every excuse to not do it, until Horo lays into him.
In fact for once Lawrence does everything right. He involves her like a proper partner from the start. He does all the leg-work skillfully. He tells her the plain truth (even that the barmaid flirted with him). And so on.
Horo really is the one to blame here. She pushes his buttons to get him to do it. She ignores his requests for advice and involvement, essentially forcing him to everything on his own. She even plays the "I trust you completely" card. There is something unsettling about her behavior, not Lawrence's. Is she trying to get him into trouble? I suppose he could have continued to say "no, I won't do it", but he knows once her mind is set on something he'll inevitably lose.
If you want to be mad at Lawrence for letting Horo get into this mess, fine. But in the final conclusion, his only real fault was finally listening to her and trusting her against his better judgment. You know, that thing he was bitten on the hand for not doing earlier in the season?
If things go ill, he's most certainly going to have to buy her back. But he will be the one with the right to get angry with her, not the other way around. But you know he won't, because this is Lawrence. The guy can't get her angry at her even if she nearly ruins his life.