But surely you wouldn't argue that someone handing over their wallet in exchange for not being shot was consensual, even if the person really truly preferred being a little poorer to being dead. So presumably your opinion would be that they did not have the third option, which is to say "no, i'd rather not give you my money /or/ be shot" and walk away.
No, I wouldn't say that was consensual. But I didn't think we were talking about cases where one of the "negotiators" uses or threatens force against the other.
However, since we cannot walk away from the table of "making a living" completely -- (those born landless are forced to sell our labor to the owning class to literally survive) there must be mechanisms for making that relationship as equal as possible.
You are equating the use or threat of force, which is illegitimate, with not getting the benefits if you opt out of a deal, which is legitimate. It will always be the case that if you opt out of a mutually beneficial deal, you will lose the benefits that deal would have given you.