Why wouldn't a police officer enforce the law? I do not get this.
An officer armed with a deadly weapon should be used to enforce a very narrow set of laws. People make terrible generalists - we are best when we specialize. We let the IRS handle tax problems, health inspectors handle food laws, and fire inspectors handle code violations. Your average local beat cop should not be expected to enforce every law - and yes, their mandate should be primarily focused on keeping the locals happy. Everyone needs to feel comfortable relying on the local cops or they fail to do their primary job. As an example, an illegal immigrant should be able to go to the cops if they are the victim of a violent crime. If they know that they will be thrown out of the country if they report a mugging, they will not report the mugging and we all suffer.
In this particular case, let the state/local tax board send over an investigator when someone calls in to complain that someone is selling cigarettes without paying their taxes.