More than 20 years ago when I worked a retail job in college we did verify every bill >= $20. It was easy: a simple marker revealed if it was counterfeit, along

More than 20 years ago when I worked a retail job in college we did verify every bill >= $20. It was easy: a simple marker revealed if it was counterfeit, along with something that revealed watermarks etc. It wasn't much friction, it took a few seconds.