There are two types of open houses that Realtors host to help them build their business and give a "positive spin" to their attempts to sell homes in the St Louis area.
This type of open house it typically on weekend afternoons. Contrary to the hopes of the homes seller, this type of open house is rarely the venue in which the buyer is procured. Generally, the visitors to the open house are future prospective home buyers that haven't begun their search yet, and neighbors in the area that are curious about the condition of the home or about area market information.
The future prospective buyer's are usually not working with a buyer's agent yet, most likely haven't been pre-approved and they simply attended the open house because they saw a sign or advertisement. When the time comes to buy, they could be looking in different areas and at different price points. This presents an opportunity for the Realtor hosting the open house as they may be able to gain the acquaintence of this prospective buyer and help them begin their home buying process.
The other opportunity for the Realtor is a chance to meet the homes neighbors. Some neighbors are just bored, but some may be considering selling in the future, and could use the services of a professional Realtor in the future as well. Many Realtors have special "attendance prizes" for neighbors that are filled with self-promotion.
This type of open house developed from the mostly defunct practice of Realtors called "touring". In St Louis, tours generally occur on Tuesday, and real estate offices would hold their company meetings in the morning, then all agents would be asked to visit homes listed on their companies pre-arranged home tour. This practice would give the homes seller the impression that there had been a great deal of activity, since they would see the sign in sheet filled with the names of Realtors. Often times, tours are attended by agents that didn't have anything else to do and were not working with buyer's that would be a fit for the homes. While its always possible that an agent could see a home during a tour then bring a buyer back (certainly the seller's wish) the agents are much more likely to work with the MLS to pull up listings based on buyer's criteria.
In modern times, there are still some Agent Open Houses that may even feature a free lunch or other incentive for agents to attend. Sometimes these events are hosted by Title Companies, Building Inspectors or Mortgage Lenders, so that they can mingle with the collection of agents that attend.
Most Realtors don't describe the practice of public or agent open houses as mere gimmicks as they are herein. They have become a legitimate part of the real estate industry and are used by most full-service listing agents. It is our belief that most seller's want open houses "just in case" that right buyer wanders in, and most Realtors won't argue about that!