Make sure to get as much info about the customer as possible including the CVV2 digits, in order to prevent claims of Identity Theft.
If the software is downloaded provide some mechanism to prove this has happened and that the user installed the app. Perhaps provide a crippled version that they must register, once that happens you can prove they got and installed the app.
You can always contest the chargeback.
And finally day dream but don't actually carry out:
"you messed me about, but I've got your credit card details, opps a script kiddie compromised my system. Now where did I leave those numbers?"