Can our buyer representative's negotiate a house that he listed?

It is not a conflict as long as he tells you that he has the listing. It will mean that he will get double the commission for selling the property. The seller of that home entered into a listing agreement with the agent, probably agreeing to a 6% commission. That 6% is split between the listing agent and the selling agent (buyer's agent). In this case, he would get the full 6%. If you are uncomfortable with this situation, you can ask him to refer you to another agent in his office. He will still get a referral fee from the referred agent, but you will have someone that represents you, not the seller. If you are not too familiar with real estate, I would recommend getting your own agent or having this agent refer a coworker. Remember that this agent has signed an agreement with the seller to have their best interests in mind when negotiating a contract.