Speaking with Mayor Stuart Crosby and chief executive Gary Poole, Cr Robson looked at the possible options for the money, whether to write a cheque or buy something to for the council to use.
"Let's just say I need 9000 votes to get re elected and I only get 6000, I would give a third of the $150,000 to the city. What I could do is provide the city council with two electric cars, and I'll pay for the maintenance for the first three years."
Cr Robson made a similar promise for next month's election - but this time it was all or nothing.
"[As mayor] I will lead and deliver a budget that delivers a sustainable city, so it addresses the issue of ever-increasing rates faster than inflation and ever-increasing debt," he said.
A sustainable budget meant keeping rate increases for the average residential property below inflation for 10 years.
"If I don't deliver, the whole term of my mayoralty I will do for nothing - which is the same as giving $300,000 to the city," Mr Robson said.
The money would be kept in a trust account.
"Money is not the reason I do the job."
Mr Robson's accountant, Raewyn Taylor, said Mr Robson had not touched the account containing his current earnings.
Mayor Stuart Crosby said it was up to Mr Robson where the money, if there was any, would go.
"It depends on the election figures how much money he will give back but there many good causes in our city to make a contribution to," Mr Crosby said.
Robson's money back guarantee
2016 election: "I guarantee to deliver real change for the people of Tauranga, including keeping budgeted residential rate rises below inflation from 2018 until 2028. If I fail, I will not stand for re-election in 2019 and I will return all monies paid to me as mayor"
- John Robson's election profile statement