Carl Vince, of family business Prestige Auctions Grimsby, said that "euphoria" erupted as the event's centrepiece, which had received no bids, was snapped up online right after he brought down his hammer yesterday.
Because nobody else had made an offer, Mr Vince said that he was able to accept the bid which came through late due to the website being so busy.
Mr Vince, 46, said: "It was the star of the auction, it was an item we really wished we could sell.
"We asked for interest in the room and there was nothing, and nothing online.
"I went down, I actually brought my hammer down as not sold."
But he added: "As I brought the hammer down a bid came through online.
"The cheer in the room was unbelievable.
"And it sort of went from that to a telephone call within three to four minutes - 'Oh my God, what have I done?'
"It was the chap who had made the mistake."
Mr Vince said that the bid is legally binding, with the man facing a £245,000 bill when various fees are taken into account.
His company, which has only been running seven months and got the Pleasure Island job after a recommendation, is now in talks with legal experts and Bid on This, the live online auctioneer site which was used during the March 7 and 8 auction.
But he hopes an amicable solution is in the pipeline, as two other parties have expressed interest in the carousel following the publicity.
He said: "There is a moral side, let's forget the legal side.
"We're a small, family-run business from Grimsby. What we are not in the business of is ruining people's lives.
"He's probably a family man just like me."
But he warned others using online bidding sites to take the process seriously.
"It was a crazy thing to do," he said.
"What people need to understand is just because you are sat behind a keyboard, it doesn't make any difference to the terms and conditions."
Only five items of the 1,260 lots up for sale at the auction were not taken up. Among those sold were the dodgems for £9,500, the cycle monorail for £5,000, and the electric monorail, which went to scrap for £4,500.
Pleasure Island Family Theme Park closed permanently at the end of the 2016 season.
For generations, Yorkshire families enjoyed the park during stays at surrounding holiday sites.