"Duh!", right? Well if it's that obvious, then why aren't you doing it?
My parents shop at a store that sells crafts. There's always a long line. There's always a long line because it takes for-freakin-forever to pay the store. I don't know what system they're using in that store, but I do know that their system doesn't work. I'd rather have my fingernails pulled out than shop in that store. It would take less time.
Have you ever bought anything in a furniture store? Have you ever financed your purchase? Heaven help you. You wander around for hours picking out the perfect sofa and then you sit around for hours trying to pay for it. And all the time you're thinking, "I want to give you $500, why won't you take it?"
How do you buy things from Apple?
Step one: You click the "buy" button.
Step two: (there is no step two).
Examine how your customers pay you. Reduce the process to the least number of steps possible. Then make of the steps as small as possible. Don't make it hard for your customers to give you their money. It's not polite and it's not smart.