A Phoenix hiking store owner explains who would install a slackline across a canyon and the standards they would have to meet. The in-depth look into the criteria comes days after investigators said a helicopter hit a recreational slackline south of Superior on Friday, leading to a crash that killed all four on board. Arizona Hiking Shack owner Dale Stewart said customers looking to complete a long stretch need to ask the right questions to complete their purchase. Molly McBride has more…