I haven't gone over $2 million, but I can tell you that both the buyers and the sellers of property over $1 million, seem to be more difficult and require a lot more ego massaging than those buying less expensive property.
If the get a hint of the other side being 'difficult' it can become a pis*ing contest between the two to see who can win. Those can be difficult situations, and the agents need to work closely together to make sure that everyone stays on the same side.
I had a buyer threaten to throw my seller out of the window when we were at the closing table for a $2 million dollar property. It didn't close.