Esther tells Dwight the deal to buy the tractor is unfair unless it's based on mileage. Unlike automobiles, tractors record usage based on hours, not miles.
When Pam visits Brian to ask him how much footage they got, even when their mic packs were turned off, Brian states that they use parabolic mics during shooting. In Goodbye, Michael (2011), when Michael leaves for Colorado, he takes his mic off at the airport and gives it to the production crew. From that point on there is no sound as Michael says farewell to the crew and turns around to walk to his terminal. About 5-7 seconds later Pam rushes in bare foot with her shoes in her hands then hugs and talks to him with no sound from any parabolic mics.
However, the production crew may not have anticipated the need for a parabolic mic, as they would not have know Pam would show up as she did.
The tractor Dwight is buying is a Case IH, but the logos on the hood are obscured, presumably because of licensing concerns. However, there is a sticker on the roll bar that is visible in the shot of Clark sitting on the tractor that clearly displays the Case IH logo.