There is a sign on the door and in the store that plainly says they do not accept credit cards. The reason they are cheap is that they keep their costs down by not supplying bags (which stores pay over a million dollars a year for if they are a big corporation), they do not pay credit card processing fees by not taking cards, they charge a deposit for use of their carts, which is smart, and they make you unload your cart to the belt, also smart.
People complain all the time about how expensive things are, but they never take into account how much it costs to run a business. Aldi also does not allow their customers to abuse their employees, which is another plus in my book. If you want fancy, go elsewhere.