There is one idea we haven't talked about yet. Registered mail through the postal service. When Alice sends her money to Bob,she sends it via registered mail. Bob has to sign for it or he doesn't get it. And if he signs for it that makes him obligated to carry out his end of the deal or Alice can take him to court.
I think that in the place where I live it is forbidden to send cash through the postal service.
I did not know that, if you refer to the country I have in mind. Crazy.
Goes in line with the fact that using cash for more then 2000.- is forbidden in Spain and in Italy it's a even lower limit with 1000.-. There are high fines when using cash above those limits. Crazy...
In Spain as far as I know the Banks are sending all your financial data to the tax authority end of the year. So you have zero privacy in your financial life beside using cash in limited amounts.