In a hot market, aka a "sellers market", rates are low, money readily available, housing inventory low, and demand high. It's not rocket science, and in fact, the only thing the buyer is likely to need from his agent is advice on price. Is it possible the fair price attracts a buyer on day one? Sure. But it's far more likely the house should have been listed higher. Perhaps a lot higher.
(Disclosure - I am an agent) I'd rather set a price too high, and agree with the seller that we have room to go down, than to sell on day one at a low price, wondering how much money I just lost my client.
Even if an offer came at asking price on the first day, in a hot market, the right answer is "we are entertaining a number of offers, please confirm your best and final by next Friday."