Before completing checkout? So they billed your credit card without permission? That's pretty damn bad... Like maybe credit card fraud bad.
I haven't dove down into fraud statutes too much but I'm going to go out on a limb and assume that when someone takes payment they have a legal obligation to verify the credit card holder actually authorized the payment they collect. At the very least Visa,etc,'s lawyers will care. There are also a whole bunch of other statutes that can apply too.