Dealing with fraud and liability?
Tangurena: You've got 2 major risks here.Your question indicates you're concerned about someone using a bogus card, using your site, and then you're out the money/fees (this is indistinguishable from a chargeback due to an unhappy customer). As far as I can tell, this is a "cost of doing business" and other than some common sense rules (don't accept business from Nigerians, East Europeans, or whoever is the "land of hackers" this week - check the address and IP addresses - log everything), I don't think anyone will be able to assist you (including law enforcement, who has a hard time getting involved for less than 6-digits of losses). One of the applications I'm responsible for accepts/processes credit cards, and we have 0 chargebacks, but that's mainly because this application is a add-on for a desktop application that costs several hundred dollars.The other one you didn't seem to address is PCI-DSS compliance. If you store the credit card number in any place (including log files), you (and your customers) could be in for a world of hurt if you're hacked (like TJ Maxx did). 
https://www.pcisecuritystandards.org/index.shtml (see chart on page 4 of the spec, and the checklists at the end may be helpful as well).