Kostis is a golf instructor and has been a member of the Golf Digest teaching staff for over 20 years. Among his many students are Paul Casey, Chez Reavie, Bernhard Langer, Steve Elkington, Dan Marino, Maury Povich, and Mike Schmidt. He and Gary McCord are partners in the Grayhawk Learning Center in Scottsdale, Arizona.
He lives with his wife, Sandy, and their two children in Paradise Valley, Arizona.
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