yeah joomla is cool, good for lots of stuff, but all the plugins are pretty much out tha box, so unless you know about programing and shit there aint much you can do to customize em to look like your not just using some freeware plugin. I used Joomla to make a few sites but after some problems with clients and their hosting providers I found it is easier for me to just write simple applications from scratch to accommodate stuff like content management. For a cart option I prefer to send the users to a storefront on Paypal or something similar depending on who the client is working with. That way the end user knows they can trust the transaction and you dont have to deal with all the bs of running a secure server or storing credit card info. Depends on the requirements of the client really, but in order to limit my liability I push for hosting the storefront on a trusted site.