SEO is not always that straight-forward. There are many SEO agencies that will offer companies services to improve their SERP visibility however, some agencies (and individuals) do not play by the rules and there is such a thing as being penalized by Google for your SEO methods, this is through black hat techniques, there are also more genuine white hat techniques. These techniques are analysed to offer companies direction to keep their SEO know-how up to Google's standards.
White hat SEO, otherwise known as ethical SEO is the practice following search engines rules and regulations to create organic search results.
Black hat SEO, otherwise known as unethical SEO, disregards rules and regulations applied by search engine results.
Google penalties happen from either two ways, manually or algorithmic. Manually from someone from Google's team detecting unnatural links on your webpage, regardless of what has been found as unnatural on your page, it is your job to fix the problem and re-submit your website for reconsideration for Google's search results (Bigcommerce, 2015).
It must be noted that today's white hat SEO rules may in the future become black hat SEO rules, allowing the two conflicting sides to somewhat learn from each other (Mangala, 2008). Furthermore, white hat approachers should not ignore the black hats as there could be important lessons to be learnt from them (Mangala, 2010).