Chance the Rapper,—Carlos Santana, Jethro Tull. Tricia Cleppe watched them all slip through her fingers. She wasn’t—about to let Dave Chappelle do the same. Since Cleppe moved to Denver last August from Washington, D.C., she’s been determined to see a show at Red Rocks Amphitheatre without surrendering—to the second-hand ticket market’s ransom-like price gouging.