Anchor is the text part of a link between the opening tag <a> and the closing tag </a>.
In addition to the link juice, which each link without nofollow attribute passes, the anchor text allows search engines to more accurately understand what the link page is about. Thus, the effectiveness of the link building depends on the anchor text.
Search engines are struggling with artificial impact on search results, which include link building and other violation of Webmaster Guidelines. In relation to link building, Google penalty is a punishment against a website for excessive link building.
However, It is not always possible to determine algorithmically the artificiality of the links themselves, but it is possible to very accurately determine the artificiality of the anchors. Therefore, in order to avoid Google Penalty, try to make anchors as natural as possible and for sure relevant to the target page.
Avoid using commercial words such as buy, order, services, etc in anchors and remember that the most natural non-commercial anchors should be the dominant anchors in your backlinks profile.