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Some stuff I look for in a quality link: Pagerank/MozRank Other links on page - are there any pill/viagra or gambling/porn links?  Anything else fishy?  Skip it if so.  Are there more than 50-100 outbound links on the page?  That's a lot. Google cache date - has it been cached within the last couple of weeks?  The more recent the better. Is the site relevant to your niche?  What about the domain?  Does it look like a dropped site?  If so skip it. How easy is it to get a link?  Do they automatically take reciprocals? And like Adam said, how is the content? All of these factors can help, but really it also comes down to your gut feeling.