In the glossary of wrestling terms, a ‘Smart’ is someone who has inside knowledge of the business.
They want to feel like insiders and gain access to exclusive information. However, they will also use this information to attack the company publicly if they feel upset.
Large customer communities tend to attract Smarts too. These are people who know the history of the community, know how the company is faring and might be privy to insider information or disputes from current or former staff members.
They can easily cause the most grief by sharing negative (trusted) opinions about the community and its progress.
If you want a good example of how to communicate with smarts, read this update from StackOverflow. If you want to know what happens if you drop the ball, read the comments.