In the SEO sphere, we tend to differentiate between two types of SEOs / SEO techniques.
White Hat SEO and Black Hat SEO.
Doctor Jekyll and Mister Hyde.
One would be good, in accordance with Google's recommendations (in particular), the other would be bad and risky because it would play with the weaknesses of search engine algorithms.

White, gray and black hat seo are three completely different ways of approaching the SEO of a site.
Why does black hat seo offer much faster results and how is it dangerous for your site?

White hat seo is a set of natural referencing and optimization practices that respect the official recommendations of Google, the leader in internet research.
The latter aim in particular to:
improve the technical performance of the site, for example by having a consistent page architecture or by reducing the loading time on mobile
strengthen the user experience
work on the quality of editorial content
White hat seo is therefore a set of processes considered “ethical” by search engines.
These go in particular in the direction of Google which constantly seeks to reinforce the relevance and the quality of the results which it proposes.
It is therefore indeed a long-term visibility strategy.
If it requires a little time before offering results, they are on the other hand lasting.

Black hat seo is a set of processes and automations aimed at exploiting flaws in algorithms to manipulate the results in its favor.
The results can therefore be surprising.
Sites engaged in such practices can find themselves on the first Google page overnight, or even in first position.
With such results, it is obviously tempting.
But any loophole must inevitably be filled, Google constantly carrying out more or less important updates of its algorithm.
When the flaw is corrected, which is never very long, all those who have used it to artificially climb the SERPS are then unmasked by Google and sanctioned.
Depending on the importance of the questionable practices used, this ranges from decommissioning to the complete disappearance of the site.

Gray Hat SEO uses many techniques to try to improve the SEO of a site while respecting a certain ethics and a certain quality.
He strives in particular not to exceed the dangerous limits set by Google such as the use of exact anchors in its backlinks or the duplication of content.
If we stick to Google's guidelines, any action aimed at optimizing its SEO, in addition to the technical optimization of its site and the creation of original content, is assimilated to Black Hat SEO because it is then intended to influence the algorithm.
Therefore, the slightest sponsored article or the slightest directory sheet created would be enough to bring a site into the category of those using Black Hat SEO practices.
Fortunately, in practice Google is much more flexible on this subject, which is not the case for its employees, whose mission is to manually analyze sites that could rely on questionable practices.

Since 2011 and the deployment of filters such as Penguin then Panda, Google has clearly shown its desire to purge all poor quality sites from its results.
This includes those who attempt to manipulate its algorithm through automatic or fraudulent seo practices.

Black hat seo techniques are all banned by search engines.
Some have been particularly sanctioned in recent years:
cloacking which consists of the use of scripts to display different content, depending on whether the visitor is a robot or a human.
The indexed page is therefore different from the page seen by Internet users
the concealment of text and keywords in its pages: the editorial content of each page allows search engines to understand their theme.
The richness of the lexical field used then makes it possible to appear on the most important expressions.
It can therefore be tempting to add a long list of keywords to make sure you are well positioned, while hiding them behind an image or using a font color identical to that of the background.
keyword stuffing which consists of the excessive accumulation of keywords in a text or in Hn tags
the duplication of content from other sites by simply copying and pasting a competitor's text to display it on their own
the use of bot to massively and automatically generate links in comments of articles or blog
the massive generation of external links pointing to the same site

Google's algorithm is originally based on the number of external links pointing to the same site.
At its beginnings, the engine considers that the more links you have, the more you are a reference in your field.
Logically, therefore, you should be in the top search results.
Netlinking is a common practice that is an integral part of any good SEO strategy.
On the other hand, its abuse which consists in massively generating hundreds or thousands of links to improve its positioning in the results are sanctioned by Google.
Nothing more normal in itself since these poor quality and artificial links (directories, purchases of links or domains, etc.) have only one goal, to manipulate its algorithm.
In 2013, Interflora suddenly disappeared from the results, following a Google penalty.
In question, the massive purchase by the sign of bad quality inbound links.
Interflora then has no other choice than to proceed with a massive disavowal of all the links acquired artificially.

The use of black hat techniques or prohibited by Google is always very risky.
Many renowned companies and brands have learned this the hard way.
BMW, Ricoh and Interflora are on the very long list of structures that have temporarily or completely disappeared from the results of the web giant.
Indeed, Google sanctions are essentially of two kinds:
loss of positioning: the site goes back several pages.
Downshifting results in complete loss of visibility
blacklisting: this is the most severe sanction since it is neither more nor less the removal of the offending site from the results.
A Google penalty that is sometimes never lifted.
For a company, this can mean considerable economic weakness

Black Hat SEO is often associated with automation while White Hat SEO is touted as a technique that is not, suggesting that automation is bound to be bad for SEO.
In fact, a good SEO respecting the guidelines imposed by Google can quite automate some tedious or repetitive tasks.
This is for example the case for automatic redirects, 404 error detections, internal meshing or integrations of web users' requests in a section of their page, essential tasks that can be completely automated without the risk of infringing. the Google guidelines.
It is understood that BlackHat techniques present risks for the medium and long term visibility of your site, and today very few companies will offer you this type of service.

SEO.fr for example only offers WhiteHat services in correlation with Google guides.