I had my own experience buying my first home, the new construction condo agent told me that I didn't have to have a buyer's agent and could just deal with them but the more I did my research the more I realized that my agent would be legally required to represent my best interests and could do a better job advising me on a process that might seem intimidating to a first time buyer.
I can understand why some of these sellers said "YES!" when someone knocks on their door and offers them cash that's equivalent to a lifetime's worth of savings but there is some fault to be assigned to seller's who don't do their due diligence. If someone says they'll pay cash right away to you, you have to think that perhaps you should see if there are other buyers in the market.
The article mentions that the buyer's agent find another buyer who will pay more than Buyer #1. So, what's the problem with that?
The buyer's agent has a fiduciary duty to the buyer, not to the seller. If the buyer's agent convinces the seller to sell at a price below market, and then finds Buyer #2 to buy at market, and Buyer #1 picks up the profits, that's a great agent ... for the buyer.
The seller should have his own agent, who's job it is to find the highest bidder and to not sell below market.