Even most of the superstores charge this. This is illegal and unethical. Don't think that bigger is necessarily better. Think about it. To them, it probably doesn't matter.
Most stores are indifferent.
Some even make more if you do return the computer. First of all, it is illegal in Massachusetts to post a cash price for anything. Secondly it is just plain unethical and misleading. PCs for Everyone always posts the higher credit card price. At PCs for Everyone you will never have to pay more just because you are using a credit card.