Sorry, what is your actual objection here? I'm not saying anyone should be forced to sell below market price - I'm saying the market price is inflated by the the cost of land: Land that no one created, land that is not a product of any human market.
The point of a Georgist land-value tax is to separate the value of the land from the value of buildings on the land. Land itself is a public good and should be taxed as such.