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I want to start a discussion about assessing the true value of a backlink. Here's a scenario: I've just started working on SEO for a new client. Once I've got the strategy stuff out of the way, I like to start by looking at backlinks that competitors have. I use Moz OSE (and other tools) and filter by followed links to the root domain. This gives a good starting sense of where competitors are getting links from. As I start to explore those links, I see some black-hat (or grey-hat) practices at play: display:none links, footer links, sidebar links, comment spam, etc. The problem I have is, there seems to be no way of knowing whether or not those links are responsible for boosting the competitors rankings. They come from sites that have good DA and PA, yet we're told that tactics like display:none and comment spam will either get those links devalued or may cause some sort of manual action. My question is, how do others evaluate the full spectrum of the value a link has that goes beyond trust, authority, and citation flow?