It is very difficult to make a statement about the industry because it is questionable what SEO actually is. Some get confused because most SEO companies keep their methods and strategies secret. We have a situation, every company is completely different and produces very different results so it is important to keep it a secret in order to be successful.
Fact 1: There is no one-size-fits-all SEO methodology. It is basically defined as the process of increasing traffic from the SERP to a site by Wikipedia. Of course, the real question of how they do this is a debate. You can navigate to this website if you are in search of further information about SEO.
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Fact 2: SEO campaign basically depends upon the website structure, keywords, website content. It also depends on the methodology used and the popularity of the website. A website cannot simply be classified as a random keyword. If your site doesn't provide a value to users, it's likely that it won't rank.
Fact 3: Some companies perform search engine optimization, while others perform search engine manipulation. But everything is marketed as SEO. Unethical optimizations yield results by all means but always in the short term (usually ending in the blocked domain name). Whereas ethical optimization opens the website to search engines and offers long-term benefits to the owner.
Fact 4: Most of the SEO companies are paid to make your website rank. If it is not ranking then they have to do the necessary changes but unfortunately, this is not what is happening in the industry.
Some SEO companies implement some strategies on your website and move on to their next client in the Hope that the site will rank. Even if it won’t, they will have more customers. So, choose the company wisely in order to obtain results.