An online store is a 24 hour active revenue machine, it should accurately display and describe your products and services in a professional manner to give you the best opportunity for each and every sale. Your success depends on this.
Now, don't get the wrong idea, a site design does not need to be full flash, loads of custom images and special entry pages, look at Google, they have a nice logo and a clean understandable landing page. Depending on your target market, you may only need text to make your sales, but the text still needs to be clearly layed out and understandable. It's always best to carefully study and consider the designer for your website. Make sure he/she is prepared to show you many examples and ask many questions about your needs. They should ask for example sites that you like and work to your budget, not up-sell you special Flash graphics. If you are working with an ecommerce website shopping cart then it's advisable that you keep all design services and software technology within the one company as it's important for the designer to know the capabilities of the shopping cart software they need to work on.
Design layout.
Layout of a website is extremely important to the ease of navigation for your customers. Their product of choice should only be within 3 clicks from the home page. Be sure to to have an easy to use category menu and obvious product titles with good descriptions directly below. Always aim to cross sell in your product pages with thumbnails of related items.
If you are using custom graphics or flash design, make sure this is kelp to a minimum in a shopping cart and only serves as a quick impressive display of professionalism rather than showing off how much money you have. Your design needs to look professional for one important reason. If your site looks like it was built yesterday and could easily be taken down today because you obviously don't care about the look of your business, then why would your customers be comfortable in spending money with you. Trust level is a big reason for customers parting with their hard earned money.
Remember, you only have one chance to make a first impression. If a visitor comes to your site and doesn't like what they see, their gone and there's a good chance they'll never come back