A chartered surveyor approached by three men accused of trying to "buy" the Ritz in London for £200m, said the price was beyond his "wildest dreams".
Christian Sweeting refused to progress the deal unless provided with a £30m bond, which never materialised.
The prosecution allege Conn Farrell, Patrick Dolan and Anthony Lee tried fraudulently to sell the Ritz for £250m when it is by the Barclay brothers.
All three deny conspiracy to defraud at Southwark Crown Court.
The jury heard that Mr Dolan, 68, of Philip Lane, Tottenham; Mr Farrell, 57, of Cambridge Road, Aldershot, Hampshire, and Mr Lee, 49, of Broad Lane, Goole, East Yorkshire, "sucked in" trophy property buyers Terence Collins and Dutch financier Marcus Boerkhoorn.
They claimed to have a deal to buy the Ritz in Piccadilly for £200m and that could sell the hotel, which is valued at £600m, for £250m to them as they had a "close friendship" with the billionaire brothers.
Mr Collins and Mr Boerkhoorn gave the three men £1m as deposit to secure the deal, the court heard.
Mr Sweeting, who worked for property investment firm London and Central European Investments Ltd (LCEIL), told the jury: "Not in my wildest dreams would I have expected that anyone would have access to a contract to purchase that asset for £200m."
He said that Mr Lee and Mr Dolan had repeatedly asked him for a letter saying they had the contract to sell The Ritz, but he refused to speak to anybody in the hotel unless the bond was provided.
He added that he doubted Mr Lee's credibility when he found out that he was involved in a property deal in Cambridgeshire, which Mr Sweeting described as a "complete fiasco".
Under cross-examination by Nicholas Johnson, for Mr Lee, Mr Sweeting said he was not in a position to offer a contract but could have "opened a door".
He added that he was embarrassed about his role in the alleged scam.
"It impacts upon my professional reputation, completely.
"When Mr Dolan came to see me, I wish I had not even entered into discussions with him about anything, frankly," he added.
The case continues.