Thank you all for the answers. It confirm what I thought. There is still a need for 3rd party for "real" (physical) transactions.
Face to Face transactions would not require a 3rd party, as the transaction occurs directly between two individuals.
Are you sure ?
I have thought about it and I have come to the conclusion that yes, we must have a third party.
Maybe I'm wrong, here is my reasoning.
Let's say I sell to you a highly expansive painting. We will set an appointment. The day comes. I'm putting the painting in my car.
I met you. But I don't know you. Maybe you have a gun ? If you have a gun and I don't, it will be very easy for you to steel my painting without paying. (there is no police here because police is a 3rd party)
So, I will grab a gun AND a 2nd man with a gun also, to be sure that my painting is safe.
But you will make the same reasoning on your side. So you will come with your gun plus a friend and a machine gun, or a riffle.
And I will make the same reasoning, and so, I will have to come with at least the same destruction capacity than the value of the painting, so that it neutralize any wish to steel it.
So we will both come with huge fire power and men to help us. Those men can be considered 3rd party.
That's a kind of byzantine general problem.But, in fact, it cost too much to deal transactions that way. So we will both give our guns to a 3rd party that will be set as judge in case of conflict. It's a 3rd party, and economically it's the only (is it ?) solution ...
Anyway, no matter how I try, I alway end up with a 3rd party for real transactions. There is no way any algorithm can help us. Unless we can built an automated justice with a robocop.
Do you agree ?