How do they transact if they don't trust each other? You have the guarantee that the money your received is not going back but what kind of guarantee does the r

How do they transact if they don't trust each other? You have the guarantee that the money your received is not going back but what kind of guarantee does the receiver of product/service has? Yes - so far, it worked well for extortion with ransomware but is that something that we want to have? Can you think of a legit business case where the merchant providing the promised service is guaranteed and all you need is a method to receive the payment? All that when the merchant and the buyer don't trust each other at all and on't have a conflict resolution mechanism. What do they trade exactly?