"The hardest thing for me is to differentiate the people who contact me, to find out if they're real," says Lenz. "They can get very annoyed, but I need to know they can write the check."
Ah, the check. Sometimes there is no need. After all, when an international jet-setter pays $100 million for a third or fourth home, why take out a mortgage?
Many top-tier transactions are "done in cash," says Condon.
As for which mega-mansion will sell first, it's anyone's guess. The decision to purchase a home of such caliber comes down, more than anything, to personal preference.
"Think of it this way," says Umansky. "I could put three mega-yachts in a line -- one contemporary, one traditional and one Mediterranean. I don't know which one is going to sell because I don't know which one Larry Ellison or Bill Gates is going to pick."