Trade Me has cracked down on the top bidders on a $100 bill put up for auction as a joke. The top bid earlier this morning was $5150, however the online site has since removed this bid and taken it down to the smaller figure of $295 -- a value that is still almost three times the bill's value.

Ashburton man Robbie Shefford had earlier said if the top bidder made true on the more than $5000 bid that he'd donate it to a charity close to his heart: the Ronald McDonald House, where he'd spent some time when his youngest daughter Lilly-Anne was born.

But he had always been sceptical about the larger bids.

"It would be awesome if the bidder was genuine, but I can't imagine it."

LISTEN: Robbie Shefford speaks with Tim Dower

Mr Shefford said if he ever saw the money he'd donate it to the charity that had helped during his daughter's six-week hospital stay.

He said the auction, which he'd started as a bit of a joke on Boxing Day, had gone well above his expectations.

"The comment was made, 'I wonder what will happen if you put it up on Trade Me with a $20 reserve and a $150 buy now'," he said. "I didn't think it was going to go this mental."

If anything he thought he'd lose money in the auction.

Bids on the "unwanted Christmas gift", hit $5150 early this morning.

There were 98 bids in total, with 117,378 page views and 1895 people had added the auction to their watchlists.

Bidding closes on Saturday at 4.57pm.

Mr Shefford engaged with 205 people on the site who had asked questions about the auction.

One person asked if he would consider selling for $80, to which he replied: "Yeah, sweet as, it will be 20 bucks post and packaging."

The thread of conversation showed an attempt by the seller to bring one of the top bidders, Jackson93 out of the game, by removing his initial bid.

When questioned, Mr Shefford said: "this is a fair auction, I have something for sale. The winning bidder will own it. All unrealistic [bids] have been removed."

Jackson93 put in his final bid of $5100 at 11:12pm yesterday, but this was superseded this morning by poppaelf with a bid of $5150.

A Trade Me spokesman said contact would be made with bidders to make sure everyone was "playing by the rules".

Any bids that weren't genuine would be withdrawn.