The "perception of cronyism" during former mayor Ken Livingstone's term has eroded the trust in City Hall, Labour challenger Oona King has said.
Ms King added that if elected she would bring in an independent body to vet mayoral appointments.
Mr Livingstone said inquiries by police and internal investigations had cleared his administration of cronyism.
He told BBC One's the Politics Show that he will fight the government's plans for cuts "as I fought Thatcher".
Former Bethnal Green MP Ms King accused her rival of "cronyism" over his former race advisor Lee Jasper who faced allegations about funding irregularities. Mr Jasper was cleared by police and City Hall.
She said: "I don't think we can deny that the perception was and remains that there were people at City Hall who were channelling funds to organisations they knew, their friends, and what we need to do is to restore trust.
"I think there has been a perception of cronyism without the shadow of a doubt.
"So that's why I am proposing a tough new appointments commission that would vet any of my appointments."
She added: "Ken has often said that if you just took out Bromley, Bexley, Hillingdon, and Havering then the result would have been different.
"But you can't just take those boroughs out. It's 370,000 people, it's 15% of the electorate."
Mr Livingstone hit back on the "cronyism" issue saying "it was a perception".
"A two-year police investigation found there was no wrongdoing- no cronyism and no wrongdoing."
Mr Jasper quit ahead of the 2008 election after the publication of intimate messages to a female colleague.
Mr Livingstone also said that he will "fight cuts".
"I will be working with trade unions and Labour councils to defend services.
"I will fight those (cuts) as I fought Thatcher.
"I am not running on the basis of cooperating with this government to make cuts in public services, I am running on the basis of defending them," he added.
Ms King said spending on housing - on registered social landlords - could be cut.
She said there are "things you can cut around... the services that are not frontline services."
In September, the Labour Party will choose the candidate to challenge Conservative Mayor Boris Johnson.