The situation is as follows: a kind person sent a letter that he noticed on one of the sites the unfair promotion of one of our sites (text block with a link to our site). The letter describes what the consequences may be, up to the site's ban search engines. Also casual services are offered in high-quality promotion.
Maybe this letter would have gone unnoticed, but we really ordered the promotion of this site. The performers firmly assert that they use “such” methods.
For our part, we searched for links to our site from the left sites (sites of unknown subjects). There are several dozen such links.
Actually questions: who to believe? How to check the artist?
Maybe someone faced with a similar situation.