This is what all these cities that say they won't arrest non-violent offenders can expect. As long as they don't assault anyone they can get away with anything.
No law says a customer cannot stop them through any means they want, as long as its non-lethal...unless they have what appears to be a weapon OF ANY KIND where you feel your life or anyone elses is in danger...felony? I'm not a lawyer, but I recognize a crime when I see one...