Not all SEO is made equal. Some companies may promise exceptional results, but this is only because they take short cuts that could be ultimately harmful. Proper search engine optimization takes some time to develop; there aren't any easy answers.
Search Engines are looking to promote the best content long-term, and they can change their algorithms at any time. In the complex world of search, there are both good and bad techniques in SEO -- and the end doesn't always justify the means.
When SEO companies concentrate on trickery in order to quickly boost their SEO, Search Engines simply change their algorithms to alter their results. This has happened many times over the last decade, sabotaging anyone who was trying to produce overly successful results.
The only way to develop true SEO is to provide the content that search engine companies truly want to promote. This requires a very thorough understanding of the goals of the search engine companies and what they are interested in: useful, interesting, and unique content. A solid Search Engine Optimization Company is going to understand what a search engine is looking for and the best way to present this.
Though bad SEO practices can sometimes offer some fast results, not only are they not long-lasting but they can result in a company being blacklisted and having their results permanently removed. True SEO takes a long time to develop, as the search engines want to make sure that the content remains high value and consistent.
Bad SEO tactics range from misrepresenting the content of a website to the search engine itself, to trying to trick users into clicking and visiting their links. Regardless, these bad SEO tactics nearly always serve to mislead the user in some way rather than giving them the information that they are trying to get.
These SEO tactics can be as advanced as creating entire networks of poor quality sites, all devoted towards the singular goal of just getting as many hits as possible. But this is also a problem as hits alone cannot make a website successful; someone tricked into visiting a website is unlikely to actually use it.
All of this together shows that there are both good and bad practices when it comes to developing Search Engine Optimization. The best companies will focus only on the generally accepted practices for improvement, while others will try to take short cuts that are ultimately self-defeating.