When I was a bartender, customers would often rack up huge tabs over several hours, ordering martinis at the busiest moments and shots for everyone at the bar minutes before closing. The most ostentatious customers were usually the ones who would ditch the bar without closing their tabs, and 90% of the time, those cards would decline. It's a risky scam, but people who work in the service industry know better than most that customers can be shockingly audacious. As much as we wish we could expos…