The best advertising is a happy customer. The New York Times reports that Amazon.com is giving up on television advertising in favor of word-of-mouth advertising. Amazon finds that spending the money on offering free shipping on orders over $25 is more cost-effective.

Now Amazon has turned its quantitative prowess on one of the most vexing questions in marketing: Is television advertising worth the expense? Amazon's answer is no. And it has canceled plans for any television or general-purpose print advertising this year. The company is so sure of its decision that it has dismantled its five-member advertising department, assigning the employees to other roles.

If you are anything like the typical retailer, at least half of your business is coming from repeat customers. Keeping them happy is the best investment you can make.