When it comes to modern SEO, there are many myths surrounding the best practice methods to implement to your campaign. There are forums and sites all around the World, which give an individual perspective on the way to do things and not to do things.
One thing is for sure, SEO is an art every bit as much as a science. Some sites I look at give damning reviews about so called 'Black Hat' techniques. True, there are some big no no's when it comes to SEO, but many optimisation companies go too far when describing the rules in SEO.
Who decides what works? Which rules work better for which websites? Where is the set of laws of for SEO? Well, there is no bible for SEO, and I have found over the last 5 years that it is very much a suck it and see kind of industry. Getting the right blend of SEO techniques differs for every industry, and that's why it's such an interesting and varied method of marketing.