However, you may encounter pages with a large amount of spammed forum discussions or spammed user comments. We’ll consider a comment or forum discussion to be “spammed” if someone posts unrelated comments which are not intended to help other users, but rather to advertise a product or create a link to a website. Frequently these comments are posted by a “bot” rather than a real person. Spammed comments are easy to recognize. They may include Ads, download, or other links, or sometimes just short strings of text unrelated to the topic, such as “Good,” “Hello,” “I’m new here,” “How are you today,” etc. Webmasters should find and remove this content because it is a bad user experience.
QUOTE: “Tell visitors clearly that the page they’re looking for can’t be found. Use language that is friendly and inviting. Make sure your 404 page uses the same look and feel (including navigation) as the rest of your site. Consider adding links to your most popular articles or posts, as well as a link to your site’s home page. Think about providing a way for users to report a broken link. No matter how beautiful and useful your custom 404 page, you probably don’t want it to appear in Google search results. In order to prevent 404 pages from being indexed by Google and other search engines, make sure that your webserver returns an actual 404 HTTP status code when a missing page is requested.” Google, 2018
Yes, you need to build links to your site to acquire more PageRank, or Google ‘juice’ – or what we now call domain authority or trust. Google is a link-based search engine – it does not quite understand ‘good’ or ‘quality’ content – but it does understand ‘popular’ content. It can also usually identify poor, or THIN CONTENT – and it penalises your site for that – or – at least – it takes away the traffic you once had with an algorithm change. Google doesn’t like calling actions the take a ‘penalty’ – it doesn’t look good. They blame your ranking drops on their engineers getting better at identifying quality content or links, or the inverse – low-quality content and unnatural links. If they do take action your site for paid links – they call this a ‘Manual Action’ and you will get notified about it in Webmaster Tools if you sign up.