Well, suppose one of the operators wanted to cheat the system(they are the only ones who could). There are only two ways he could do it, collecting money that hasn't really been sent or not dispersing money that has been sent.
Say Operator A fraudulently 'sends' $100 to be picked up at Operator B's place. Then A's compatriot goes to B and picks up the dough. Has Operator A made any money? No because They generally use a running tally of debt and repayment to settle up, rather than any money actually changing hands. In other words B is out a hundred bucks but he has also debited A for that amount, its a wash. If A's compatriot makes off with the money then it is A that gets shafted.
As for the other way, not dispersing money that has been sent, if I send money and it never gets to the intended recepient, Cousin Akbar will call me up and tell me so and I will go all over town telling people not to send money via Mid-Eastern Union. Only the honest money senders would survive in an industry so totally predicated on trust.
I guess there is a third way, thats quitting the business while I'm in the red on the running tally and not settling my debt before I run off to Fiji(and even then its only by that amount that you've benefited and even this risk you could minimize by never letting the tallies get too imbalanced). I suppose staffing the network with blood relatives would also cut down on the flight risk.
The article says that the faraway recipient, is identified by name or just a code number. A secret code could make fraudulent receiving of money impossible. Say for instance when Operator A sends Operator B the message to disperse X amount of money to me he sends it encrypted in my PGP public key block, only when I(the intended receiver) come along with my private key can the message be decoded and Operator B knows without a shadow of a doubt that I am the legitimate receiver.