A couple of articles about the two shows that sold out within minutes of going on sale:
The Cincinnati Enquirer "Buffett tickets gone in minutes"
It continues Buffett’s streak of sold-out Riverbend concerts dating back to 1987, when he moved his show from Kings Island’s Timberwolf Amphitheater and its 10,000 capacity, to Riverbend’s 20,500 capacity. "There has never been a Buffett show here that didn’t sell out, almost always in 15 minutes or less," Moehring said.
Pittsburgh Channel.com: "Jimmy Buffett Show Sells Out Quickly