The only supported e-commerce solution I've ever seen for Unix is RedHat's E-Commerce Suite. I was running some web sites a while back and we needed a dozen or so e-commerce sites. I spent a long time researching Unix-based ones, but they all reeked. Finally had to go with an NT (*shudder*) solution. The credit-card fulfillment was a large part of the problem. But the RedHat solution came out after then. It's been going for a few years now, so I would assume that it's reasonably good.