Without a contract, the buyer is clearly not a client. She is a customer . A contract makes a difference in other ways. For example, there are things the seller may not want disclosed to the buyer such as their urgency to sell, which could compromise their bargaining position. An agent who then discloses this information is in ethical violation and can be brought before the state review board on charges.
Some offenses are serious enough to have licensure to practice revoked.
But the buyer has no such protections without a contract. Anything they say to an uncontracted agent may be passed along to the seller. Because, any agent who works for the buyer without a contract automatically becomes a sub-agent for the listing agent, and is therefore working on behalf of the seller . It's all spelled out - in the listing contract and in the buyer's representation agreement. A contract makes the difference in whether you are a customer or a client in the real estate transaction.