Concerning the entire subject of Asmachta kania or lo kania: The Halacha seems to follow the opinion that Asmachta lo Kania.
Does this mean that if for example one were forced to and ultimately agreed , to pay a broker or business partner employee a certain commission or percentage that he never really originally intended or even wanted to, could he then later (after the deal went through etc. and there is no risk of him losing the deal) come and say I am not obligated to pay you as I never really meant to do so. or even wanted to, in the first place?
I Understand that "Asmachta" means OUR assumption of what he had in mind, I am asking if he came out and said it, and there is cause to believe him as he was forced to accept those terms against his will.
Asmachta is a very involved Sugya, and this is not a forum for properly dealing with the entire issue. I will try to deal only with what directly relates to your question.
The general rule is Kol d'Iy Lo Kana, which loosely translated means that contingent Kinyanim are not valid. However there are many qualifying rules. One which is brought in the Gemara Bava Metzia 70a as explained by Tosfos is that it is only an Asmachta if the condition is in his power to fulfill.
Simply stated, we call a conditional Kinyan "Asmachta" only if the person made the condition meaning to keep his side of the condition. In such a case, the person can claim that he never really expected that the condition will not be fulfilled (and that he will become obligated by the other side of the condition). For example, if someone says, "If I do not do such-and-such I will pay you a certain sum," and he was sure that he would be able to do such-and-such, it is assumed (in certain circumstances) that he never actually intended to pay. However, if the condition was, "If *YOU* do such-and-such I will pay," we cannot assume anything, since whether or not the condition is met is out of the hands of the one who made the condition. Therefore he has to live up to his promise and keep the condition. The fact that he says he did really mean what he said is irrelevant, since it is "Devarim shebe'Lev.