The technician needs to come to the door, introduce him or herself, and make sure their feet don't track dirt in your home. I wear booties over my shoes and this is a lot better than walking in a customer's home in stocking feet.
Because you tend to use the thermostat, make sure the technician goes there first to check it out and replace the batteries if necessary. If it's an older thermostat, don't be surprised, or offended if he suggests a new one. A defective thermostat causes a lot of no heats and batteries are a huge culprit behind that. The furnace needs to checked for carbon monoxide, the burners, pilot, cabinet, drains cleaned and inspected. If there's a flame sensor that should be cleaned or replaced at your expense if worn. The hot surface ignitor also need to be checked and if worn, replaced. The filter and humidifier pad are likewise. The wiring should also be inspected and the thermostat lugs tightened, and any burned, worn or brittle sections noted on the tune up sheet (your contractor does have a tune up sheet, right?) When the furnace is running, he needs to check and set the fuel pressure, check amp draws, and the heat rise of your equipment. The heat rise is the difference between the return and supply temperatures and once he's done, the cabinet wiped down and the work area cleaned. He or she also needs to document everything they did and show you. You also need to understand that if you don't do the work the tech recommends and the furnace calls it quits, don't go screaming to the contractor they didn't do their job. You didn't do yours. If you go for the cheapest contractors, then you really have no one to blame save yourself. You get what you pay for. Maranatha!