As with any sales agreement, a "deal" is made when a willing seller and a willing buyer agree on the conditions of a sale.  If a property has "hit" the MLS, they're usually a commission split between the "listing" agent and the "selling" agent.  I agree with some of your statements and disagree with some of them.  

Real estate agents have two tasks: a) convince the seller that the sales price and conditions are to his or her benefit and b) convince the buyer that the sales price and conditions are to his or her's benefit.  If they can't do that, there will be no sale and no commission.  When we've bought properties I've always made it clear that no one is our "buyer's" agent.. we represent ourselves.  If we sell a property, we don't list it exclusively with anyone.  We notify agents and tell them to bring us a "single party" purchase offer and, if the deal works, we'll pay 3%.  This has worked quite well for us.
"Sweetheart Deals" do, unfortunatel,happen and they're very unfair