I would disagree that an agent is self serving by trying to get the most money for the person the agent works for. A listing agents jobs is not to get the best deal for the buyer. I would not tell the seller to take or decline an offer, I would only tell them what they will net from the amount and remind them of market conditions, etc.
Is this offer enough? No, I find out what they need and suggest a counter. If the offer amount and what the seller will net is OK, I work to get it to close. But do not think because I am looking out for the interests of my client, I am self serving-I am only doing my job. If i was working as a buyers agent for you, I would make sure I represented you in the best way possible.
Andrew is correct you are in competition with the REALTOR since they work for the seller and their job is to get the most money in the shortest time and with the least amount of hassle to the seller. I would not say they will fight you, they will want the transaction to close, but not at the expense of the client they work for, which is not you.
Any conversations about the property are by the contract between the listing agent and seller supposed to go thru the agent. You are asking the seller to violate a contract to enter into a contract with you. If the seller will violate the contract with the agent, what makes you think the seller won't also do the same to you? Kharma is a b*&^%
Andrew is also correct if the seller is responsible for paying the agent, of course the agent will have to sue the seller. Or if they have enough time, the agent can put a lien on the property so they must be paid before it can close.
Understanding agency, and who the agent works for is the biggest misconception of most people.