Mr Flynn said he didn't feel the need to "take care" about receiving £50,000 from Mr Tom Gilmartin because he "trusted" the developer.
Ms Patricia Dillon SC, for the tribunal, pointed out that Mr Gilmartin had made serious allegations to the politician several months before the £50,000 payment was made in May/June 1989.
As a result, Mr Flynn had initiated a Garda inquiry and spoken to the taoiseach, Mr Haughey.
She asked Mr Flynn whether it had occurred to him that, in the light of these allegations, he should record the payment in order to show there was no question of impropriety.
Mr Flynn replied that the payment was a political contribution by Mr Gilmartin to him, and both men agreed this was the case.
But Ms Dillon said this was a "monstrous, enormous sum" in the light of what Mr Flynn was earning at the time. Did it not cross his mind to make sure there was a receipt?
Mr Flynn said Mr Gilmartin had not asked for a receipt. If he had asked for a receipt, he would have got one.
Counsel asked whether, in the light of the fact that allegations had been made against a member of his own party, it didn't occur to the witness to say "hold on, I'd better take care".
"I didn't have to take care because I trusted Mr Gilmartin," Mr Flynn replied.
Earlier, Mr Flynn said he first met Mr Gilmartin in November 1987 in relation to the developer's plans to build a shopping centre at Bachelor's Walk in Dublin.
He described this as "an exceptional proposal on a prime site". He encouraged the developer to go on with the project and was sure it would be a "huge success" for Dublin and remove an existing "eyesore".
Mr Flynn said he was anxious for Bachelor's Walk to go ahead but it didn't.
"I'm very sorry it didn't come off," he commented.
He rejected Mr Gilmartin's account of an alleged meeting with the taoiseach, Mr Haughey, and government ministers in Leinster House in February 1989.
"The meeting as described by Tom Gilmartin could not have taken place," Mr Flynn said. He had no recollection of attending such a meeting.
When it was put to him that Ms Mary O'Rourke recalled being invited by Mr Flynn to go and meet Mr Gilmartin, who was in the company of other ministers, Mr Flynn said Ms O'Rourke's evidence was in "direct conflict" with that of Mr Gilmartin.
Asked if her evidence was incorrect, he said he had no recollection of going to Ms O'Rourke's office to invite her to meet the developer.
He would not have sympathised with her on the death of her mother, as had been claimed, when this event had taken place three months previously. If he had sympathised with her, it would have been in the immediate aftermath, seeing as he met Ms O'Rourke every day at work.
Mr Flynn said Mr Gilmartin "did like to complain a lot" in their meetings. He was a very affable man but he was also in a hurry and wanted things to happen in a hurry.
Mr Flynn said he would point out the "inevitability of gradualness" in local authority matters, but Mr Gilmartin would complain.
