The authority's finding said Birdling — a former police officer and soldier — claimed he didn't see his client because he was on the phone to a bidder, who eventually bought the three-bedroom townhouse for $451,000.
The widow had previously said she expected offers of around $550,000.
However, the agents' authority said it was "incomprehensible that the licensee [Birdling] did not see or was not made aware of the complainant's emotional state ... before he left to negotiate with the buyer", particularly as other Bayleys staff were aware of her distress.
When the bidding failed to meet the reserve of $540,000, Birdling spoke to the bidders in the room, and the phone bidder, before taking a written offer to the widow from the highest bidder.
Two hours later, she signed the offer.
"There is ample evidence that the licensee was dealing with an old, vulnerable woman and was well aware of this fact. At the end of the auction the complainant was clearly distressed," the authority found.
"The complainant's options should have been outlined in far more detail. Time should have been offered to her and the suggestion of consulting her son should have been put forward. None of this took place, and pressure, not particularly subtle at that, was applied to the complainant to accept the offer the licensee had obtained from the highest bidder.
"But the complainant clearly was not coping. The licensee had an obligation, in our view, to respond accordingly. He failed to do so."
The authority also said Bayleys had enough senior staff present at the time to have "stopped the auction and suggested it be cancelled in view of the state of the complainant".
The agency "should have intervened and properly supervised the licensee. Accordingly, their failure to do so means that they have failed to discharge their obligations ... and are guilty of unsatisfactory conduct."
Allegations of selling to a personal acquaintance, failure to provide for an on-site auction, that the agent had a conflict of interest in the sale, and that excessive commission was charged, were dismissed by the authority.