Black hat SEO is a tactic applied to manipulate Google algorithms for better ranking on the SERP like adding inappropriate or inaccurate information, fake reviews, rankings, etc. Such practice lacks trust. You should avoid black-hat SEO services, as Google can detect your site and ban it.
Search engines like Google and Bing hate black-hat SEO techniques as the results obtained by applying these techniques often deliver poor quality or duplicate content, false backlinks, spam comments, and content stuffed with keywords. The site becomes unreliable.