Developer Owen O'Callaghan finished his direct evidence to the Mahon Tribunal by denying he had ever made a corrupt payment.
Mr O'Callaghan said he does not whether to believe his former lobbyist Frank Dunlop, who said he bribed politicians to get Quarryvale rezoned.
Mr O'Callaghan hired Mr Dunlop as his lobbyist for the Quarryvale development and paid him a total of £1.8m.
The tribunal heard that when Mr Dunlop was originally investigated by the inquiry in 1998 he denied any corruption, but he changed his evidence in 2000 and has testified in 15 modules about systematic bribery of councillors.
Although Mr Dunlop said he bribed councillors during the Quarryvale rezoning, he said Mr O'Callaghan was not aware of this.
Mr O'Callaghan agreed to pay Mr Dunlop £300,000 in 1998 because of his difficulties with the Revenue Commissioners, which resulted from tribunal inquiries. And he paid £300,000 towards Mr Dunlop's tribunal legal fees until he heard about his claims that he had paid bribes.
Mr O'Callaghan said he does not know whether to believe Mr Dunlop's claims of corruption.
He said he never sought an assurance from Mr Dunlop that the fees he was paid were not used for corruption.
But Mr O'Callaghan said he did not believe a word from his former partner in Quarryvale Tom Gilmartin, who he described as an outrageous, notorious liar and fantasist.
He said Mr Gilmartin had made his allegations of corruption because Quarryvale succeeded without him.
Under questioning by Patricia Dillon SC, Mr O'Callaghan said he could not explain how allegations made by Mr Gilmartin in 1998 were later confirmed by Mr Dunlop's testimony in 2000.
Mr Gilmartin had told the inquiry then to look at payments made to Mr Dunlop through Shefran Ltd and named three politicians - Liam Lawlor, Colm McGrath and Sean Gilbride - that Mr Dunlop later said he had bribed.
Mr O'Callaghan said he had made payments to these politicians in recognition of their support for Quarryvale, but denied they were corrupt.
He could not explain where Mr Gilmartin was getting his information other than it was a wild guess or that he was being used by one of two journalists.
Mr O'Callaghan said he himself was not 'quite sure' if he believed Mr Dunlop's testimony about corrupt payments.
Questioned by Judge Gerard Keys, Mr O'Callaghan said he could not explain why Mr Dunlop would destroy his name and his reputation by making up such allegations.