scam alert!!!! cash back don't fall for it!!

I've personally had something similiar happen at Walmart. But I asked for the cash back (before they started charging an ATM fee on transactions). The cashier pulled a slight of hand on me. She reached into the change drawer pulled out the twenty, and when I was pulling the bags off the counter, rolled up my receipt and went to hand it to my wife, stopped, then handed it to me. When I got home I pulled the receipt out and no $20. Called the store to complain. Three days later, after all the tills were totalled for that day, seems the one till came up missing a few bucks more. I got my $20, the store enacted a policy of having the cashiers write their initials on the receipts with cash back, with the cash back written on the receipt with the initials and the cash back handed seperately from the receipt.