Comment Takings clause (Score 2) 70
Buying a patent by the government is merely invalidating that patent, something a government can do for free, theoretically.
That depends on the country's takings law. I'm more familiar with the United States Constitution, which provides: "nor shall private property be taken for public use, without just compensation." Canada's Expropriation Act (fact sheet) likewise guarantees market value to the property owner.