Have them not touch the CC#. Leave that last part of the funnel to some certified external. You'd also make them a big service. I simply abandon most carts if the CC entry stage is still on the merchant site and not on someone's big and recognized like PayPal, and I hate PayPal. I just don't trust the little, unknown, guys with CC# & details.
I'm never very bothered handing out my CC details. It's not like I'm liable for anything that happens with it, and when shopping online I generally just the one-time use numbers that all of my credit cards offer. Really, the worst that can generally happen is that I have to get a new CC #.