I see now. Yes, using a contact form for this sounds tempting, but that functionality is quite fancy. Contact Form 7 is so popular because it's very simple and generally works.
I've been tempted to use WP for ecommerce, and I've searched and tested a lot of stuff. Nothing looks great to me. The most popular one, WP-Ecommerce, is just amazingly full of bugs. I was actually working on a site last week that has it, and I'm thinking, maybe they've fixed the bugs by now. And months later, nope, still loads of really dumb bugs. But it basically works, so you could try that if you have a strong stomach. I would be embarrased to release a product in that kind of shape.
To me this proves that people are so eager to have anything for WP ecommerce that they're willing to use software that's about 90% baked.
I have heard better things about Eshop lately, though.
But if I were doing ecommerce, I wouldn't recommend WP in the first place. I'd use a dedicated ecommerce system. My 2 pence.