As for sellers thinking a particular agent is the best, you need to understand that if a seller thinks their agent is crap, they are effectively admitting that they could have got more.... not something people are willing to do.
I've read plenty on this forum about people who are very unhappy with their agent 
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"The greatest trick the Devil ever pulled was convincing the world he didn't exist"
In the agents case, the greatest trick is for them to convince everyone else they are genuinely caring people and will go out of their way to help others - reality is, once an agent gets the sale, they won't give two shts about the purchaser or vendor.
I beg to differ on this one too. My late mother was a highly respected local agent. She had people calling her eight years after she retired wanting to have her sell their houses. I recall clearly two cases where my mother suggested a buyer buy another house (different agent) because she knew it was a better fit for them. My mother could never have been dishonest. It was not in her nature. Because of my mother, I know plenty of agents, some of whom I would not sell with, but I also know the ones that I would sell with. In fact, it makes it difficult really because when you know a lot of agents, picking one is not easy.
We've never had an agent come to us and say "take this offer" without trying for more. However, a good agent will also have sussed out their buyer (qualified them if you prefer that term) and will have used their methods of digging gently to see "how much more" is in the pot, or if this buyer is really stretching themselves to go as high as they already have.
For our most recent sale, the buyer had buckets of money and could have paid more for the house. However, he initially offered $50K less than we took, and We all knew that he was playing us, that he knew very well the market "now" was a very different animal to the market twelve months before, but he was playing a game. Luckily, we knew how the play the game too.
We told our agent not to even bother going to paper with his stupid low offer. She suggested we ignore him and see if he came back, which he did a couple of days later with an offer that was close enough to what we wanted. More importantly, we had nobody really hot to buy at the auction, only ten days away. Better the bird in the hand, than two in the bush, especially as we got nothing from this sale. It was all going to lawyers, barristers and our brother and his son after a will challenge. The risk of not selling on auction day would have had his barrister on our backs to sell quickly after that, and we didn't want that pressure.
We toyed with trying to push him up but he was of the mindset that he had already come up $50K more than his stupidly low first offer, and we would have been asking for more only to "win". There was a risk that he would feel he had "lost face" and so we signed him up. We had issues between signing and settlement, which I could write a book about, but that is another story, and all settled as planned after much gnashing of teeth and loss of sleep.
I really do believe (as did our agent) that had we "played" this chap and pushed for more, he would have walked away. It was not a risk we were prepared to take, and some would see that as our agent accepting any offer, which we know for sure is not the case. Sometimes you must realise that many agents are pretty clever in the psychology department, and can read a buyer pretty well.
Whilst this buyer was stuffing us about, our agent found another buyer, same price which we were about to sign up (after seeing our solicitor to cut the first buyer free), when he decided he was going to play nice, after all. That is the sign of a good agent, continuing to market it and get a back up contract, just in case.
