Just to clarify this statement a little bit I believe the exact quote from Google is as follows:
“There’s almost nothing a competitor can do to harm your ranking or have your site removed from our index.”
Source: Can competitors harm ranking? – Webmaster Tools Help
Some folks look at the word “almost” and proclaim: “See… your competitor can hurt you.”
Anytime I have heard a Google engineer discuss this they cite examples of websites that were hacked or poorly moderated. Yes, a competitor can hurt your site if they get past your security features, but promoting your site with spammy links, I’ve yet to see a credible example of this.
I believe there are companies that will take your money for such a thing, however, I remain unconvinced of the effectiveness.
I have personally seen about a dozen such attempts and none of the sites I monitored suffered any rankings decline.
I believe the only thing Google does when they discover spammy links is to devalue those links and in severe cases, they may de-index the pages where those links are placed. Since you can control your own website you should not be concerned unless it is your web pages that contain the spammy links.
Google tends to hold you responsible for what is on your own website, not what is placed on websites controlled by others.
