Category - Home Selling Questions - General Home Selling FAQ's
If a Realtor is showing your home to a prospective buyer then you may allow a showing without your presence. If the buyer is a FSBO buyer then you absolutely should be there for safety reasons. Another suggestion may be to have a trusted family member or friend show the house if you're not available.
References
Courtesy of HomeOwners Advantage and link that to their entry in the wiki which is at HomeOwners Advantage