I'm very excited to introduce the Local Spam Scanner! Spam has been a problem on Google Maps forever, and it only seems to be getting worse. Depending on what categories you're working with, spam can be a real problem, often pushing your clients down the results page.
Ben Fisher, Google Platinum Product Expert, published a great guide on how to report these issues to Google. The more proof you can supply, the likelier you are to see success. Removing spammy listings is an effective local SEO tactic, especially in categories where spam seems to be rampant.
Give the spam scanner a try and see what you can find!