Atiku Abubakar, the presidential candidate of the Peoples Democratic Party, on Wednesday denied using his position as a top government official to enrich himself.
Mr Abubakar resigned in 1989 as a top official with the Nigerian Customs Service.
Host Kadaria Ahmed put Mr Abubakar under the spotlight for his purchase of private shares in a logistic firm during his days at customs, a practice that was deemed a conflict of interest.
The former vice president, however, denied the claim, saying he was allowed to purchase private shares based on existing laws at the time.
Today in Nigeria, a public official is not allowed to own or engage in private businesses, but many officials said a convention from the public service rules allows for engagement in agriculture businesses.
Mr Abubakar also denied monopolising logistics business in Nigeria after assuming office as Nigeria's vice president in 1999. He was in office until 2007.
Mr Abubakar's Intels Logistics Limited is widely deemed a major player in maritime logistics, and Ms Ahmed said the firm described itself on its website as having a monopoly in the sector.
Mr Abubakar denied operating a monopoly, saying his company might have made a mistake in describing itself as the only player in that sector.
There is fierce "competition" against Intels, Mr Abubakar said, mentioning some of the players.
Mr Abubakar's running mate, Peter Obi, was also fired with a barrage of questions surrounding his use of government funds to invest in private businesses while governor of Anambra State between 2003 and 2014.
Mr Obi denied the allegations, saying he had never enriched himself with government funds but instead invested government funds that ended up yielding so much he was able to leave a record N52 billion in government coffers.
The candidates are participating in the town hall, which is being broadcast live on NTA, ahead of the elections on February 16.
President Muhammadu Buhari and his running mate, Vice President Yemi Osinbajo, were on the programme earlier this month, during which they defended their first term and gave reasons why they deserved another.