These tips are a mashup of advice to sales people selling ecommerce web sites and for clients who use ecommerce web sites to sell or advertise products.
(1) Don't sell web sites. Sell web-based marketing/sales/PR solutions.
(2) First, do research and consultation with clients to fully understand client business, what the company is trying to do, and what the users want to know, do, and buy, and then custom build a site around that.
(3) Ecommerce sites need to contain what all other blogs, wikis, and other web sites need: About, Contact (form and email address, fax, phone, land location, cell, etc.), Profile.
(4) User observation tests are mandatory.
(5) Don't give the client what will please the client, give them what their customers actually want from a web site, and make that astonishing customer gratification and service well pleasing to the client.
(6) Consider enabling the ecommerce site visitor to customize the product you're selling, as in Flash-enable "Design Your Own" functionalities. See www.uberprints.com for an example of tee shirt customizing Flash application.
(7) If you require registration for a site, provide and explain the benefits of, and reasons for, registration. Don't just have Register and Login links.
(8) Warn web design prospects of the dangers of letting amateur, student, or well meaning friends build your web site. Explain to clients why a professional, non-generic, stable, securely hosted, customized web site is essential to achieve their business goals.
(9) Study books and blogs by Seth Godin, Kellogg Marketing Faculty at Northwestern University, Jakob Nielsen, Jared Spool, Harvey Mackay, Peter Drucker, W. Edwards Deming, John Battelle, David Weinberger, Laura and Al Ries, Debbie Weil, Tom Peters for insight, strategy, and inspiration.
(10) A blase, laid back, non-hype, casual, relaxed, friendly, no pressure approach is best, plus helping customers to compare one product versus another in your lineup, helping them decide which product to buy is where most ecommerce sites fail.