A common oversight to adding a new ceiling fan is the connection box it hangs from. Fans require a fan box rather than a standard octagon electrical box. A fan box is sturdier, made with larger #10 machine screws and lock washers to withstand the vibration and motion of the fan. It also must be secured to the building structure with proper bracing.
Keep in mind when having a fan installed that this is a requirement and retrofitting the proper box in can be an added cost that often hits people unexpectedly.