Q: When I enter credit card details, is there a way I can also enter the CVC code from the back of their card?
A: Yes, there is an option you can enable so it will show a CVC/CVV2 entry box when it prompts for other credit card details. However, be aware that this is contract to PCI compliance rules, which state that the CVV or CVC security codes cannot be stored on a computer.
If you're using version 4.3 or later, you need to disable the PCI security option for not saving the security codes for guarantee info. This is under Maintenance / Credit Cards / Security Setup.
If you're using a version prior to 4.3, go to Maintenance / Credit Card Processing Setup, and check the box for "CVV2/CVC enabled". It will be one of the few options on that dialog that are still available even if you don't enable credit card processing.