Back in the late 80's I worked for a muffler and brake shop. EPA was doing stings and handing out $10,000 fines to those shops deleting convertors. Most often they would pose as customers coming in for an exhaust repair, pulling in with a test tube in place of a convertor. If the shop refused to work on the car unless a new one was installed they were fine. If they did the work bamo... Put a few shops out of business.