robdwoods - 5:11 pm on Mar 8, 2010 (gmt 0)

Can competitors harm ranking? There's almost nothing a competitor can do to harm your ranking or have your site removed from our index.

While it's true that there's a small chance of competitors harming your ranking by buying links to your site there is a much greater opportunity for them to harm your reputation. I've seen link building campaigns against sites that house negative reviews of a company. A competitor will link build against that third party site to make it appear in the SERPs for a search on your brand. There is virtually no downside to the link buying in this case as the company buying them can't be punished by a penalty, only the site housing the negative reviews.