As much as webmasters want the feature, there is currently no provision by Google to flag spam links to a website. This is because Google doesn’t take into account if it has been been created by the webmaster or not. Although Google claims that their algorithm is good enough such that one competitor cannot hurt another, it poses a serious risk of website being exploited by competitors.
Video: Google explains the linking system
Hopefully Google comes up with a more reasonable flagging system to prevent third party link spamming.