These sales are done this way for tax purposes usually. The notion of hiding a sales price isn't out of the question. If I use the MLS price, then I would explain that there is a calculated price that is lower.
My take on high end property and why I do not do them, is that there is a very big element of this kind of garbage and in reality, there is a case to be made for a bunch of "Blue Sky" - which is an argument that has been made upon occasion. ALL property will contain a BEV.
There is no way that many of these super priced properties A - COST (plus land value) what they bring. (negative depreciation???) or B - can you really allocate this to the LAND? (A very von Thünen sort of idea.)
http://geography.about.com/od/urbaneconomicgeography/a/vonthunen.htm
Someone is giving a premium for the ambiance or status of a property. That is nearly impossible to quantify. It is like trying to value a Rembrandt that someone just discovered in their attic in Amsterdam last year...as a sort of one-of-a-kind property, the sky is the limit...or rather the pocketbook of someone who just has to have it.
One of the "Koch Brothers" that isn't active in the political "Koch Brothers" is a big buyer of Western Memorabilia. For people like that, if they want it, then price is no object. They will outbid any museum in the world.
So we have this whacky upscale market that is the result of the proliferation of the extreme wealthy class in America and the huge number of new buyers of that sort of property....people with no real concept of "value" because they come from China, Venezuela, or are fleeing high taxes like the French. Otherwise, they are filthy rich Americans who made it on Wall Street or Silicon Valley - the nouveau riche who define the very words "conspicuous consumption".
I really don't think "Value" has any meaning in such a market. It is a very inefficient market where fad and style may dominate the thinking over "value".