Developing a sound SEO strategy and implementing it is no easy task, but you do have a key benchmark to judge your success: traffic and sales. If your strategy worked, more people will be coming to your site and, with that greater audience, your sales should have increased as well. But what about your competitors?
It's easy to track your own stats because you have access to your logs, server info, etc. Keeping track of what the other marketers in your niche are doing is not quite so easy, unless, of course,