the radicalXChange people have revitalized a somewhat older idea, harberger taxation. The mechanism is relatively straight forward, people self-assess the value of their stuff and pay a periodical tax on it. At any point in time, anyone can force the sale of said commodity.
Point being that if someone sets the price at above market rate, they're reducing allocative efficiency (by exercising monopoly power over their property) so they pay a tax. If goods are exchanged at market rate, then that improves the utilization of the property.