Eric Hartley: Nickel and dimed

As he sold his new tax plan during a barnstorming tour of Maryland last month, Gov. Martin O'Malley repeatedly stressed its "fairness."

That's because sales taxes are going up, but property taxes are going down, along with income taxes for all but the richest 4 percent.

"The vast majority of Maryland families will be paying less," Mr. O'Malley said during an event in Ellicott City, one of seven stops he made in nine days.

But that's an assumption resting on some dubious and suspiciously precise numbers. And the truth is, a lot of...