Here are some tips and general etiquette notes that will help you be a more savvy shopper when it comes to visiting open houses.
Always sign in. If you are working with an agent, protocol is to have your agent call the listing agent ahead of your visit to advise that they have a customer who will be visiting and they will relay your name so that the person hosting the open house will anticipate that you are already working with another sales agent. When you arrive at the open house, please indicate your agent's name on the guest list.
There are two main reasons why an agent will host an open house, the first and most obvious is to give the best service to their client, the homeowner, by actively showing the house and making it easily available for viewing. The second reason is to grow and cultivate a list of prospective home buyers, so if you are "just browsing", please let the host agent know it up front to avoid confusion at a later point.
If you are a potential buyer, you might want to know that a good buyer's agent will accompany you to open houses rather than send you out on your own, so don't hesitate to ask them to go along with you for that extra set of eyes and ears.
If you attend an open house on your own, and you are not currently working with another agent, and you like the house, it is not necessary for you to get another agent in order to make an offer and negotiate the purchase. The agent you meet at the open house will be more than happy to facilitate the transaction for you.
While you are walking through the house, generally you will be free to roam on your own, but if you prefer to have a tour, just ask. The attending agent wants you to feel comfortable while you are looking. In fact, they want you to feel at home.
Ask all the questions you want of the agent, but bear in mind there are some things that you are best to learn on your own. If you want to know about the quality of the school system, that information is generally public, or if crime rates are a concern to you, contact the local law enforcement agency.
Remember that painting is an easy job, so if you don't like the color of the walls, it is easy to repaint before you move in. Do not let the color of the walls detract you from an otherwise suitable home. This same principle holds true for carpeting and light fixtures. Replacing a carpet or a light fixture is easily done and can be a relatively low-cost improvement to make in your new home, and it will help you on your way to making it your home.
Enjoy your browsing, get a sense of how you feel when you are looking through a house, ask questions, and you will find most agents more than happy to have you come back for a second look if the house feels right to you.