How does Wanna Cry verify payment Reports indicate that there are three default addresses to which victims of Wanna Cry are asked to send funds. 

Assuming that Wanna Cry actually does decrypt once payment is verified, how can the software know that the specific computer is the one that should be decrypted in association with the victim's payment?
IIRC WannaCry requires you to contact the malware authors (via their built in chat system thing) and then tell them the address that you used to send the payment. Then they will manually decrypt your files for you. Otherwise there is no way for them to track who sent what payment. This of course is fraught with issues and is very unreliable. I have heard some people say that their files were decrypted even without paying, and others say that they have paid but their files were not decrypted.