Competitors might click paid listings in an attempt to waste advertisers' marketing budgets. To add insult to injury, the brazen ones attack advertisers head on by bidding on advertisers' trademarks and redirecting traffic to their own web sites.
Trademark owners who are not already aware of this problem are going to soon get a shocking wake-up call. Many still aren't marketing their branded terms on the search engines, let alone policing the space for their competitors. While trademark owners sleep their customers are being wooed away.