Ho Chi Minh's negotiaters spent years arguing about the tabe to be used and wouldn't let the real talks start until it was settled.
Of Course, when Nixon took office, he simply sent B-52 Bombers into North Vietnam and started hitting the targest that Johnson forbade. Shortly after that, Ho Chi Minh decided that the size, shape and color of the table didn't matter, heck, he no longer cared if there was a table, just as long as he could get the bombs to stop.
Personally, I think Teddie Roosevelt had it right "Talk softly and carry a big stick". Talks always seem to come out better for your side if you have good military strength and the otherside does not doubt your will to use it. If the military option is taken off the table or is not credible, then the otherside has no incentive to negotiate in good faith.
In the case of the negotiations with Iran, there is not really a credible military option. Most of Europe has shown that they will not back military operations, The French will probably block any UN actions, not to mention the Russian Federation which shares a border with Iran (and has recently been trending back towards it's Soviet ways). So of the larger Players, that leaves the US and Britain, both of which currently have internal problems and "leaders" who are considered unlikely to actually use military force. That leaves Israel, they have the guts and determination to do it, but it is really questionable if they have the means if going it alone. Israel has a very fine military, but it is small and thus it is questionable if they could actually but together a force large enough to get the job done and project it that far from their border. I personally believe that they will try at some point. Saudi Arrabia has worked for years to try to curb and reduce Iranian influence in the Region, but since it is believed that Israel is the primary target for Iran, SA will do nothing. They want to bring down Iran, but they will not do anything that even remotely could be viewed as helping Israel (well that and the fact that although they have some of the best military equipment available, their military still sucks).
So without a credible military threat, Iran has no real interests in negotiating. Sanctions are also not a credible path. They sound good, but just like times in the past, France, Russia and China (as well as a few others) will talk out of one side of their mouth and turn around a violate the sanctions anyway. Although, France does have it's first president that is not from the socialist, so he might just buck that historical trend.