That's a smart FSDO. Yes there are cases where a private pilot can be compensated for flying a plane. The test is, are they being paid to fly or is the flying incidental to their job? A traveling salesman can be paid to fly because he's paid to travel between A and B. How he does it doesn't matter. It would be hard to argue a company would pay to have someone walk the pipeline right of way. They are hired to fly, therefore a commercial certificate is required.