They're not selling MOs. They're offering money transfer services at their stores.

http://blog.walmart.com/money-transf...prices-for-all

"Walmart-2-Walmart offers a simple and transparent fee structure with just two price points: customers can transfer up to $50 for $4.50 and up to $900 for $9.50."

Just looking at the price structure, it doesn't appear to be a MS material/vehicle.