Some buyers are just starting their search and don't have an agent yet. They are at risk of getting trapped with an agent working for the seller. (Read up on 'Procuring Cause' at Procuring Cause ) If you don't already have an agent (and let the seller's agent holding the open house know that you don't) you could be trapped into using the seller's agent. Forewarned is forearmed.
What to do: The basic idea is that when you walk through the door to look at the house you should already have an agent (THAT DOES NOT WORK FOR THE LISTING COMPANY) that you can name as your agent. That may mean having more than 1 agent (so you could not sign a contract with either) since you may want to look at a home listed by one of their companies. There is a way around having 2 agents. Use an agent with a company that exclusively represents buyers. No listings - no conflict. Full representation. A better deal.
If you don't know of a company near you google "Exclusive Buyers Agent". Don't assume all the agents that pop up are EBAs. First, look for an experienced agent that will listen to you and knows something about houses. Then, look for membership in the National Association of Exclusive Buyer Agents. Go to naeba.org This is the same site that you will find if you go to Suze Orman's site to find a buyers agent. Even HUD in their settlement cost booklet suggests (on page 6) that buyers use an exclusive buyers agent.Happy house hunting! Be safe and be represented.
Don't get trapped.