Category - Home Selling Questions - General Home Selling FAQ's
If you are marketing your home to Realtors you may decide to use a lockbox. If you are not working with Realtors then having a lockbox on your door is unnecessary. Real estate agents are bound by laws and ethics while viewing a home when the owners are not present. You should never let a non-licensed person view your home when you're not home.
References
Courtesy of HomeOwners Advantage and link that to their entry in the wiki which is at HomeOwners Advantage