One of the major facing most realtors is trust, which is likely the reason they are given so much grief from open house guests. However, having prospective buyers sign a guest book or form does not give realtors the ability to solicit that buyer. The buyer must give consent. This is a common misconception of prospective buyers about signing in. Open Houses are one way for a property to be marketed to the public - and provides on site feedback to the realtor by the consumer.
From my experience of the past several months - the buyer of each of my listings has come thru an open house. That is not an absolute statistic, but quite a change from just a few years ago - when rarely did the buyer come thru open houses. Unfortunately, there has been more cases of robberies at open houses, where one person starts talking to the realtor, and another starts looking for valuables such as watches, cash and jewelry. If you've listed a home before most realtors will ask you to either move out your expensive items, or place them in a safe place. This is one of the reason's why realtors have taken a much stronger stance on having guests sign in at an open house. The other is to protect belongs from damage, since accidents can occur at showings.
Open houses also provide prospective sellers with an excellent way to see how their property would be sold. They get to ask questions, see marketing materials, and get a good indication of how they interact with the Realtor. Also the buyers get to see how diligent that realtor is about making sure that the public signs in; therefore, respecting that the property being sold is someone's personal home.
So next time you're asked to sign in at an open house - your one step closer to meeting a professional realtor.