The other type of change scam is say, if you were at a store and you used your debit card and requested $20 back, you would first say, could I have a $20 bill back, then change your mind to 2 10s, then 3 5s, 5 1s and a 10. You wait to change your mind after the cashier has retrieved the bills from the register so they have to think about putting the bills back from the correct slot and less and less on the math.