Competitive salary. Excellent benefits. Great support from management. Collaborative environment. Those are a few of the glowing terms reviewers use to describe Costco on Glassdoor. They are also what help the warehouse club regularly earn a spot in Glassdoor’s annual “Top 100 Places to Work” report. Why, then, did a group of Costco workers at one of its stores “overwhelmingly” vote to unionize, making it the Teamsters’ first organizing victory …