For most of us, link building is a necessity for the success of our SEO campaigns, but what types of links do we need to avoid and why?
In most cases, paid links should be avoided. Google often penalizes sites that use an obvious paid link campaign. Penalties, however, do not need to be at the site level. In other words, Google can penalize a website for certain keywords, but not for others. If Google spots a clear paid linking program for a particular keyword, your ranking for that keyword may suffer while you maintain positioning for other keywords.
Building quality links is a very labor intensive process, but that is the point. Search engines are trying to reward those of us who put in the work, not the people who try to buy their way to the top.