I've seen it many times. A business owner goes to a consultant, and they want an eCommerce offering for their products. They may even have some functionality in mind that they'll need.
But have they considered the things that will really make their website more successful? In my experience, often not.
Instead of complex shipping algorithms, extensive coupon integrations, and other struggles that often plague eCommerce websites, ensure that your clients are covering the basics.
Good photography. Succinct and engaging product descriptions. Easy to find contact information. These are three of the ten things iThemes says will help make your (or your client's) eCommerce website a success.