The short answer is no. This is straight from an email from the Maryland real estate commission that is crystal clear.
"There has been much discussion on the proper role of the agent while sitting an open house. First and foremost, there seems to be a misconception that there is some distinction under the law of agency between the listing agent and any other agent affiliated with the listing broker regarding the open house. It is absolutely clear that any agent affiliated with the listing broker who holds an open house is there exclusively as the seller's agent. This duty of loyalty to the seller is not in any way diminished just because the agent is not the listing agent. This is important because many agents have openly admitted that their primary goal in sitting an open house on behalf of the listing agent is to recruit prospective buyer clients. Such activity can be a violation of the agent's duty of loyalty to the seller."
In summary, your job at the open house is to represent that seller - and to get into dialog with as many people as you can to see if there are any prospective buyers for the seller's house. In the course of that dialog - if you're doing it correctly - you're most certainly going to run into people too early in the process to buy that house, and other people who simply don't like that house. It is perfectly okay to work to form a relationship with those people with the intention of representing them for another property.
If you have more questions on this topic or have ideas for another topic, email them to brokerhotline@kellerwilliamsdc.com