External Microphones

I'm wondering if anyone has had experience with using external microphones. I need to video real estate agents doing an introduction to their listings but am concerned about second hand noise

I haven't done it before, but from experience in other areas, I would lean toward using a wireless lapel mike. That would be much less susceptible to other noises IMHO.

I wouldn't use the camera's built in sound system for anything professional... Use a complete external recorder and lavalier mike... The recorders allow you to adjust the sound properly as well as eliminate any/all camera noises... wireless Lavaliers run about $30

I use a lapel microphone clipped to my shirt and digital voice recorder in my pocket. I copy the audio file from it over the camera's track.