Accused Colin Coats, 42, is alleged to have had a stake in the deal, the jury has been told.
Asked about some work he had been asked to do for Ms Spence, Mr Syed said: "It was some type of bond. She just wanted (it) as a prank, initially for a small amount and then she asked when it was being prepared to just add on more zeros, and she was laughing."
The witness added: "I thought she just wanted to play a prank on someone or something."
Mr Syed said he was promised £500 for the work but Ms Spence "never gave me a single penny".
Coats, David Parker, 38, Philip Wade, 42, and Paul Smith, 47, all deny murdering Ms Spence, who it is alleged was held hostage and tortured before her alleged murder.