How to Identify Bad Backlinks that Kill your Rankings?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Michael Martinez: There are many tools available but none of them are 100% reliable. Their metrics and tags are opinions. It`s not enough to say "they are opinions backed by data" (which some people do).
  
  While those opinions ARE backed by data, the data doesn`t come from the search engines whose algorithms decide which links to accept, ignore, or count against a site.
  
  If the links use the "rel=`nofollow`" attribute (which many links in blog comments and some forum discussions use), you don`t need to worry about them.
  
  If the links are published on pages blocked by "robots.txt" (which many profile links are), you don`t need to worry about them.
  
  If the links are redirected through a URL shortener that blocks robots (some but not all do this), then you don`t need to worry about those links.
  
  If the links are published on social media platforms like Facebook, Twitter, and Pinterest - those companies have taken steps to comply with the search engines` wishes that the links not be allowed to pass value. You don`t need to worry about those links.
  
  If the links are published on blog networks or in guest posts on other blogs, and if those sites are not indexed in the search engines, then you don`t need to worry about them.
  
  If your site has not received a manual action notice from the search engine, then you probably don`t need to worry about any links as the ones the search algorithms don`t trust are being ignored.
  
  But if you feel there are aggressive links using targeted, keyword-rich anchor text for no reasons other than to improve search engine rankings - especially if they are embedded in content that is irrelevant to the anchor text - then there is a remote possibility those links *MIGHT* be hurting your site. You could try disavowing them and see what happens.
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  Ahsan Sohail: Thank you so much.
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  Ahsan Sohail: What do you mean by this line? 👇
  "If the links are published on pages blocked by robots.txt (which many profile links are), you don`t need to worry about them."
  
  Are saying that Profile Creation sites block User Profile Pages through their robots.txt file?
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  Michael Martinez: Ahsan Sohail Some do.
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  Bill Hartzer: Majestic
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  Paul William: I would suggest using AHREF.
  
  Check the traffic and Google position. If it is ranking and gettting sent traffic by Goole, then the Big G approves of it.
  
  Also look at the alt text pointing into it. If your linking site is full of spammy alt text such as xxx content, weight loss pills or Viagra then its a bad link.
  
  You can also check Wayback machine. Was the site ever a spammy site that sold links?