I remember when many scammers used this method to get money. It was also the best way to transfer money to another country in incognito mode. There was a controversy with this service in my country. They said for example it helps drug dealers to move money in foreign countries.
I have heard about scammers using WU to send money and later complain to WU that transactions were fraudulent in an attempt to recover the money, or would do things like use credit cards, whose payments are later disputed, legitimately or otherwise.