FWIW, as someone who has the same problem with fraud folks at $DayJob you really do need to go with a service to deal with that sort of thing unfortunately. We

FWIW, as someone who has the same problem with fraud folks at $DayJob you really do need to go with a service to deal with that sort of thing unfortunately. We use an internal tool from our parent company but yeah, you don't really have a choice but to assume a good chunk of your customerbase will try to cheat you. Similarly, as long as the checksum is valid you should "complete" the order and handle follow up with issues [e.g. Card declined] at a later date. This can just be automated via email, with a 24 hour delay. Honest typos won't pass the checksum, fraudsters will and the delay in the "failed authorization" also helps a good deal in discouraging such activity.