The default presets used by eCart will not store Credit card details in the database or transfer the credit card number through email.
At the end of the day though, the flexibility of eCart will not prevent you as the developer from making modifications to the system that would store the information.
I want to make sure if we use eCart for Paypal or authorize net transactions, we are not storing the credit card info on our servers.
can really only be answered by you.
eCart wont store the credit card details unless you configure it to.
eCart uses 2 behaviors for storing order information, they are both added to the confirm page:
eCart Store Order Summary to database
eCart Store order Details to database
the eCart wizard will give you the option of using a preset for creating the orders and order details table or you can use your own.
The presets used by eCart will not have a column in the orders table for the credit card number or other specific credit card details. so the presets are not designed to store that info.
if you are not using a preset, though, it is quite possible to configure eCart in a non PCI compliant manner. I very strongly don't recommend it, but that doesn't mean it cant be done.
I have had people ask here in the forums before how they can store the credit card info, or send it in the receipt, i have always responded to tell them that it's a bad idea, and illegal.