The real estate firm is a giant on the Canberra property scene, with part of its business devoted to advising landlords on securing leases.
In the national capital, where public service agencies lock in office spaces for periods of 10 to 15 years, this is a lucrative business.
But a separate team within Colliers is sub-contracted by federal government agencies looking for office space, through the Department of Finance's panel of property providers.
It was this team that was engaged by the Australian Taxation Office to help secure new headquarters throughout 2020.
A parliamentary committee has since unearthed a conflict declared by Colliers at the time, when it realised its separate leasing team had advised Doma Group on potential uses for its block at 15 Sydney Avenue, Barton.
Doma had "sought and received market leasing, feasibility and building management advice from Colliers (Agency Division) to assist in preparing an offer for 15 Sydney Avenue, Barton", the Australian Taxation Office told the committee in response to a question on notice, in December 2023.
The Tax Office would go on to secure Doma's Barton site for its new office in late 2022.
This site was then sold to Charter Hall, as part of the lease agreement, for a purchase price of about $300 million according to industry sources.
Colliers declares conflict in April 2020
The issue was unpacked during an inquiry into ethics in the audit, assurance, and consultancy industry, chaired by Labor senator Deborah O'Neill.
Appearing before Parliament's Joint Committee on Corporations and Financial Services on Monday, April 22, Colliers' Nick Evans said he had been the one to declare the conflict.
"The conflict was raised on 6 April, 2020," Mr Evans, Colliers ACT chief executive, told senators.
"As soon as I became aware of the matter ... I immediately contacted the ATO as the lead in that project."
Colliers was subsequently banned from representing Doma Group as part of the Tax Office procurement process, while an independent probity advisor oversaw the procurement process.
'I have some suspicions': Deborah O'Neill
Senator O'Neill, who has been one of the key players in unravelling the PricewaterhouseCoopers tax leak scandal, has been vocal about her concerns
"We've heard all of this in so many different contexts, Mr Evans, you might understand why I have some suspicions about the effectiveness of declared protocols in comparison to practical realities," she said during Monday's hearing.
Mr Evans said the firm took separation of its teams "very seriously".
"Senator, we have rigid protocols in place from a technological perspective, from professional standards, from licensing, from staff training," he said.
"Our internal conflict management processes, not only in Colliers, but within the broader property service provider deed, mandate it.
"It's a matter that is at the forefront of our mind and it's something that we take very seriously."
In a separate statement, Colliers said it "confident that it adhered to the highest standards of probity and integrity in discharging its advisory role on the ATO relocation and in its professional dealings with Doma Group".
"Based on the probity advice, clear arrangements were put in place to avoid any potential for a conflict of interest.
"These included Colliers' Agency team withdrawing from providing advice to Doma during the relocation process; and the procurement process being subject to oversight by the probity adviser."
Finance to select new panel
Senator O'Neill has also flagged concerns about Finance's approach to property procurement, whereby it contracts to three providers, but they are able to sub-contract.
Colliers is actually engaged through another firm, Ventia.
Speaking at a Senate estimates hearing in February 2024, she told Finance officials she had "some real gaps in ... confidence in the processes that you've put in place".
Finance is in the process of seeking a new panel of property providers.
