The commissioner was responding to an appeal by Scottish homelessness charity Streetwork after it had a Freedom of Information request rejected by Glasgow City Council.
Streetwork asked to see the successful proposals submitted by two charities, Barnardo's and homelessness charity Glasgow Simon Community, to run the city's homeless outreach services.
The council, supported by the successful bidders, argued that the proposal contained trade secrets and releasing it would be likely to substantially prejudice the charities' commercial interests.
But the commissioner ruled that neither details of how the outreach service would be run nor the way the proposal document was drafted constituted trade secrets. He also denied that releasing the details would make it easier for the charities to be outbid in future.
He added that he would have ordered the release of the proposal on public interest grounds even if it had been likely to prejudice commercial interests. He said: "Disclosure has the potential to encourage competitors to develop services that encompass good practice at competitive cost, and to provide public authorities with increased value for money."
Sector groups in England were divided about the ruling, which has no force south of the border but could be taken into account in any decision by the English or Welsh information commissioners.
Jay Kennedy, policy officer at the Directory of Social Change, accepted Streetworks' argument that sharing best practice between charities was the best way to promote the welfare of vulnerable people.
He said: "Tendering for contracts is a bad way to fund charitable activity. The ultimate effect of tendering for a service such as this is that helping homeless people comes to be seen as a commercial activity."
Seb Elsworth, head of policy at chief executives body Acevo, said charities should be able to protect commercially sensitive information. He said: "Investing in developing new services will become unsustainable if it cannot give an organisation market advantage in the long run."
John Craig, director of the Innovation Exchange, said privacy was not always in the sector's interests. He said: "Sharing information is often the right thing, but it can also be the smart thing, boosting reputations, networks and know-how."