How does that make sense? If anybody can snap up your property from under your feet at any time, you are forced to value your property higher than literally every other person in existence, which is axiomatically not a fair valuation.
The "dream" is that it results in a fair valuation, but the reality is it results in rampant problems. Unless you set your valuation high enough, anyone with money who is pissed at you can cause you trouble; how much cash would you need to take to move from your house to an identical one nearby, for example?
However, if you invert it and instead say that you can sell at anytime to the agency that values your property, then it might work, because at that point the "little guy" is the one with the power.
See the winner's curse for more.