If your listing agent belongs to a fairly sizable office, an "office preview" will introduce your house to other agents working in the same office. In effect, they get a "head start" on selling your property. Once a week, the office’s agents will get together, share vehicles, and "caravan" to all of the new listings. They generally pull up in front of your house at about the same time (some even use a bus) then file quickly through your home like some bizarre "follow the leader" game.
It can be amazing to watch.
They go through very quickly, since most of them are familiar with similar models of your house. They are usually looking for anything memorable or different and to determine if your house is one they would be proud to show their clients. Then they all pile back into their cars and move on to the next house on the tour.
But some of them come back…with buyers.