IT WORKS!...I do it...I wish more agents did it...#1..had out of towners...exhausted the inventory in MLS for what they wanted...took one last drive back through Piney Z and there was a "Coming Soon" rider on an Armor realty sign. Called the agent...sellers agreed to showing...and my buyers bought the house.
#2...had seller getting his Mom's townhouse cleaned out so he could get it on the market...put up a "Coming Soon" sign...Trina Searcy was showing the neighborhood...called about it and SOLD IT...
I don't think this is a big mystery. Agents do this to generate some early interest in the property and to generate phone calls from potential home buyers. If they are circumventing the MLS rules, they could get into trouble, but they probably are fine as long they stay within the lines.
The main purpose behind coming soon is to let potential buyers and real estate agents know (not all have access to the mls) that this owner is interested in selling their home. The time it may take to place the property on the mls one could loose a potential buyer who is looking in that area and belive their is no inventory that matches their needs and settles somewhere else.
The seller may not be in the position that day to have it on the MLS but the property is actively open for offers and showings (i.e not ready for photos, may be 2 weeks out from being placed on the MLS system).
This is a great way to start marketing the property right away and not loosing a potential buyer while the other nuances are being scheduled or handled.