When Josh Beckett pitches for the Red Sox at Yankee Stadium, New York collects income tax on the portion of his salary that he earned in New York State. But what about a Boston Scientific sales representative who comes to New York to pitch medical products to a new client? New York has decided it wants a slice of that paycheck, too. Anyone who crosses a state border for work — to make a sales call, say, or meet with a client or do a road show on Wall Street — probably owes income taxes in that state. If you...