Wal-Mart is working hard to clean up its image, with new "green" stores and moves to improve its health care program.

But the chain still has a bit of a problem when it comes to the basics of retailing. Here in Wisconsin, state inspectors have uncovered a pattern of Wal-Mart stores overcharging customers. The stores charge for the weight of the packaging of bulk items, such as potatoes and coffee.

This puts Wal-Mart in violation of Wisconsin's clearly defined weights and measures rules -- so clearly that the chain is being required to pay fines of $90,000.

It is good that Wal-Mart is starting to recognize that its critics over the years -- particularly those involved with the fine group Wal-Mart Watch -- have been right about the need for the corporation to be more responsible with its workers and the environment.

But the bottom line for any retailer is how it treats consumers. And when Wal-Mart gets caught overcharging for the basics, the company tarnishes its own reputation more than any critic ever could.