crobb305 - 6:08 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.
In one of his blog comments, Matt specifically addresses the issue of competitor A harming Competitor B. I started to provide the quote here, but I am not sure if that is against TOS. Basically, he admits that they work hard to help minimize the potential, but it isn't the highest priority on the to-do list.
So, if you're in a competitive/lucrative niche, it is highly conceivable in my opinion for someone to invest in take-down tactics. It just takes time, money, and some human resources.