But this is surely an argument for better valuation rather than against the principle of forced sale per se. I'm not at all arguing that people should be forced

But this is surely an argument for better valuation rather than against the principle of forced sale per se. I'm not at all arguing that people should be forced to surrender for less than the true value, but I'm also well aware (my ex worked in this area) that each and every vendor will have an explanation for why they should get more money than it might seem at first. The customer who needs the land for whatever public good is just as restricted as the person required to sell and the whole point of this system is to ensure the seller gets a fair valuation while the customer isn't at the mercy of vendors gold-plating special cases for why they need more money.