Practice safe browsing, with the correct internet connection (i.e. it's your fault if someone manages to view your traffic over wifi when you're connected to unencrypted network)

Shopping carts provide a certain level of security. However, with the advent of attack vectors, anything is possible.

It all boils down to how safe you wanna play it. But if the site is HTTPS, no keylogger/trojan on your PC, using personal home internet, it should be fine most of the time.

^ That's the user's side of concern.

If you're worrying about the server side stuff and your reputation then choose a more stable and widely use one (Zen cart? IDK)

... and yeah, if your web app is vulnerable, your whole DB can be compromised.