It's high season for ecommerce, and showtime for shopping carts all over the world.

Good marketing managers should have spent the entire year reviewing how their checkout experience is converting customers, since a problem in the Christmas season hurts twice as much as in the summer.

Marketing Rule #1: Make it easy for the customer to buy. Specifically for shopping carts, don't do things that confuse people, cause hesitation, or prompt rework. You are delaying or losing sales.

Some Search Engine Optimization (SEO) tactics can give you a marginal boost in rankings, but hurt you on a net basis.

The main culprit is usually an overweening preoccupation with on-page keyword optimization, but link-building can hurt too.

This article is not about black-hat SEO practices, which are covered in plenty of detail elsewhere. Instead, we’ll look at “good” SEO practices when they’re overdone.

Let’s see what gets hurt.