What is the ruling on selling a property that was initially agreed upon between the agent and the buyer, then the agent informed the seller that the real estate office owner had described potential future projects for the property to the buyer, knowing that the seller suffers from obsessive-compulsive disorder and had emphasized to the agent not to resort to deception in selling? And does the burden of cheating or deception fall on the seller if it originated from the broker or agent without his knowledge?

There is no objection to what you mentioned, and you did well in forbidding your agent from cheating and deception. The sin of cheating falls on the one who commits it, not on you, because Allah Almighty says: "O you who have believed, upon you is [the responsibility for] yourselves. Those who have erred will not harm you when you have been guided" and "And no bearer of burdens will bear the burden of another." Your agent informed you of his compliance, and the office owner only mentioned what is probable, so there is no sin upon you. You should stop these whispers [of doubt], as they may ruin your life and cause you anxiety and disturbance.