Some backlinks won't get you much traffic. Others are actually harmful. Watch out for these red flags when searching for backlink opportunities, taking into consideration Google webmaster guidelines that include quality criteria. Consider that Google can also end up penalizing sites that manipulate backlinks through link buying or exchange activities to artificially grow their rankings, which is why link analysis is also so important.
1. Public link networks
A public link network is like a club you pay to join. The network will place an outbound link on its site for a fee from the link's owner. Yes, it's a link, but it's one that can earn you a penalty.Google hates these networks because they don't create value for the reader. They pack their home pages with unrelated links and have hardly any content. When Google finds these networks—and they often do, either because someone complains or because they notice that they're trying to block crawlers—they can de-index the network and shut it down.