If you are running a business for years, then I'm sure you would have faced plenty of competition, both in the online world and offline world. If your competitor hates your offline business, then he/she would probably use word-of-mouth to spread bad/negative reviews about your services or products. But, if the same happens in online business, then we have plenty of sources, it just goes on like Facebook share, Twitter Tweet, Blog posts, etc.
I came across such an incident, but this time, it involves Google AdWords ad. If someone writes a negative review about your brand/business and uses Google AdWords Ad to spread the word, then you can use this Google AdWords Trademark Complaint Form.
Trademark infringement is a serious issue, and I'm really glad Google is taking this seriously with this complaint form.