A shoeshiner would walk in front of you, 'accidentally' drop their brush. As a decent human you pick it up and hand it to them.

Then the guy insists to give you a 'free' shoe shine. After he's done, he demands payment.

The first time that happened to me, the perpetrator ruined my suede shoes. (I didn't even mind losing the few dollars for the unplanned shine otherwise..) A few days later, on the second time I didn't pick up the brush.