This article gives an overview of the Best Wordpress Ecommerce themes.
There is a perception that WordPress is a CMS, a Content Management System. It is, but ecommerce is just a particular kind of content and WordPress can rock ecommerce. Data integration into your order processing and accounting systems may take some plumbing, but nothing a slightly above average coder/plumber hasn't done a thousand times.
The nice thing about wrapping a store into WP is you get what is arguably the best CMS too. If you use SalesForce or other CRM that is another data integraiton issue you will need to budget for, but on a scale of 1 to 10 in difficulty adding a Wordpress Store isn't higher than a 5 especially if you like one of these themes.
Themes are easier than coding from scratch. These themes have almost every variation I would want as a former Ecommerce Director so find one you like and plug and play a store with a little plumbing.
Via Martin (Marty) Smith, Brian Yanish - MarketingHits.com