You are in Internet Addiction
SEO is littered with theories on how to achieve high search engine rankings, but unfortunately the factors that might affect your ranking keep changing, courtesy of the search engine algorithms.
SEO has been big business for a long time now, but a huge proportion of it is untested and more importantly CANNOT be tested, because its impossible to keep everything the same, while you test another variable.
Please note: I am not talking about optimising conversions on a page. That is measurable and provable.
Now, I have no quarrel with SEO experts who teach you what NOT to do. There are lots of very basic elements that a website should get right, JUST IN CASE they affect rankings. These are areas that cannot possibly penalise you, but might cause problems if they are not done right. For instance, missing out your meta-tags or having some of them the same for different keyword targeted pages.
But when it comes to some of the theories - well that's another matter.
If this was an open forum, I'd be getting flamed by now, but the question has got to be asked.
When folks don't understand something, or feel its out of their control, they will look for any information, or advice from an expert and a surprising proportion of people will actually go along with face-validity of a method, particularly when nobody can prove its false.
It becomes particularly powerful if a few results seem to prove a theory works, but the unfortunate truth with a theory is that it only takes one failure for the theory to have to be revised.
Even more unfortunate and in particular, referencing Google, it only takes an algorithm change to render previous SEO results next to useless, as the goal posts have changed. Worse than that, nobody really knows how they changed, although each occurrence leads to a new tranche of theories.
These are some 'truths' that I've heard over the years:
"Don't use templated pages" (various reasons)
So, if they are so bad, how come most retailers don't (or didn't) suffer ?
"Keyword density" (all sorts of theories)
Actually there has never been and is no published data on results versus keyword density and there was never likely to be - you just can't do the experiment.
Again though, there are 2 things not to do:
1. Mention the keyword so much that its blatently spammy.
2. Mention it so little that the algorithm can't figure out what you're on about.
"Target your pages carefully to keywords"
Well, this used to be true, but you only have to look at the search results to know that its changed.