This is quite true and real. Though you must be aware that this happens to every business. Adjust your prices accordingly, and only worry when it starts being a common occurrence (keep track of it). Plus, not everyone that does it is evil. People go through hard times. They might need to scrounge up some funds to pay rent this month and will do anything to survive (short of assaulting a bank). Don't demonize them. You dont know what might be happening in their lives.

Though some just are entitled assholes. Leave those alone. No sense in trying to paint the sky.