This isn't universally true. In some US states, the frequent problem is that the agent who is showing you homes (and who you tend to think of as "your agent") is not actually your agent (with fiduciary duty to you), but a subagent of the seller (with fiduciary duty to them). Here's an excerpt from recent report on this:
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For many years, a large majority of home buyers and sellers have worked with real estate agents. Most consumers believe that these agents always or almost always are required to represent the interests of the home buyer or seller with whom they are working. ... Yet, real estate agents often are not required by law to represent the interests of the buyer or seller with whom they are working, and many do not.
In reality, there are a number of different types of relationships allowed in most states between real estate agents and their clients.
• Single agent: The agent works solely for the client
and has fiduciary responsibility. A fiduciary agent
is “obligated to procure the greatest advantage to
his client.”
• Designated agent: The agent is recruited by the
listing agent to work with a buyer and has fiduciary
responsibility to that buyer.
• Subagent: The agent works with the buyer but has
fiduciary responsibility to the seller.
• Dual agent: The agent somehow is expected to represent the
interests of both the seller and buyer in a home purchase.
• Transactional agent: The agent works with both buyer and
seller to facilitate a sale but has no fiduciary
responsibility to either party.
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So while it's possible that you live in a state where you are correct, where subagency and dual-agency are forbidden, in the absence of a signed contract for the services of a buyers agent, others should not follow your advice until they are certain the same is true for them.