If the transaction is below a certain threshold (might be $1k) then you can have them send it to you using a "secret question / secret answer" instead of an ID. They just need to be sure to tell the Western Union agent that they are sending to someone without an ID, and for the WU agent to please mark that in their system. Then you'll need the person to tell you what the secret question / secret answer was so you can provide it when you go to pick up the cash.