Hello,
Some of the hottest link building techniques right now are guest posting, viral content, and link bating.
But I often see SEOs produce content that has very little relevance to the actually industry they are in. For instance, a dentist might build links by guest posting on a tech site, an attorney might create an infographic on color psychology, and an accountant might venture into celebrity gossip.
While more advanced SEOs try to make sure that the content they produce has some relevance to their industry (even if it's marginal), where is the line drawn?