Per a recent Wall Street Journal article, competing small to medium businesses with questionable ethics can have an effect on your business via online posts.  A 2011 survey shows that of consumers surveyed:

• 80% changed purchasing decisions based on negative online reviews
• 87% did the same based on positive reviews
• 69% did online research before buying
• 64% read consumer/user reviews
• 42% read articles and blogs

WSJ suggests the following:

• Be alert for rival activity — negative messages are often the same or similar across multiple sites
• Take your suspicions to site administrators
• Once posts are gone, follow-up on forums to remove any lingering suspicions (old posts can still show up on Google searches)
• If any attacks were effective, supply a Q&A on your web site or social media page
• When countering claims, keep cool — keep your tone helpful & neutral
• Develop a presence in relevant online forums early, before an attack happens — this will give you credibility when you have to respond to attacks

More here.