There's a couple of tips I can recommend.
First, get a good developer. There are several terrible eCommerce stores out there. This hurts the store's reputation and credibility. People are giving the owner their credit card or purchasing information, and if they don't trust the site, they will not trust the dealer. It's also important to maintain good usability, especially on a site as complicated as an eStore.
Second, make sure you choose a good starter package. I've seen low-cost frameworks that are much better and easy to configure than the $8,000 plus frameworks you can buy.
I recommend Amalgam Web and Media (www.amalgamweb.com
). They can set you up with an eStore at a very low cost. They'll custom design it and configure it for you, and they'll give you an easy-to-use admin tool for it so you can manage your store, items, and categories. Seriously, a complete eStore from them costs much, much less than most of the basic frameworks I've seen on the web. I suggest you check them out!