What if the supermarket where you shop rigged its cash registers to overcharge you and other customers by a few cents on every $100 worth of purchases?

Would you notice? Would you complain? Would you shell out hundreds, maybe thousands, of dollars in attorney fees and sue to recover lost – pennies?

Pennies for you, that is. Tens of thousands of dollars a year – maybe much more – for the imaginary store.

And that is why we have the class action lawsuit, a valid tool that has been misused at times but must be fine-tuned and preserved, not obliterated.

The Supreme Court of Washington recognized that this week in a pair of decisions invalidating contracts that prohibited consumers from filing class action suits over billing and service disputes. One such contract required mandatory arbitration as a resolution device; the other required that consumer actions be filed in Virginia, where class actions are not allowed.

As a result, the cases in question are headed back to the trial courts where the justice system can work as it’s supposed to.

No one should contend that class action lawsuits are a perfect strategy or that they are immune to abuse. But illnesses can be treated without sacrificing the patient.

Two years ago, after several years of political struggle, Congress treated one such illness by passing the Class Action Fairness Act. The upshot of that legislation is that class action cases affecting plaintiffs who are scattered over many states must be filed in federal rather than state courts. That’s to end the court-shopping antics of lawyers who would learn of a widespread consumer complaint, round up an affected client or two and start looking for a state judge who would “certify the class.” If only one out of tens of thousands of potential victims lived in the jurisdiction, that was good enough. If the judge then said no, the search could move on to other counties, some of which gained reputations as friendly to class actions.

That was good for trial lawyers who often were racing against other attorneys with their own clients to launch the same case. But it was unfair to defendants and many plaintiffs who found their interests being molded, and national precedents being set, at distances far from where they lived and did business.

The 2005 federal law improves the likelihood of getting such cases into the most reasonable venue.

It mitigated but didn’t eliminate some of the abuses associated with the class actions. Lawyers still tend to pocket more money than their clients, for example. (How do you think presidential candidate John Edwards can afford $400 haircuts?) There are still too many lawyers seeking clients instead of the other way around.

For consumers who want to rely on arbitration and voluntary settlements, that commendable choice should remain. But for others, class actions provide a plausible way to pursue legitimate complaints without having to risk many times more than what they stand to recoup. And they are a meaningful deterrent that exists to make unscrupulous businesses think twice before trying to cheat customers on the assumption that no individual will consider it worthwhile to take action.

Fortunately, only a sliver of businesses are that disreputable. Fortunately, we still have a means of dealing with that sliver.