Transmission Question (Mechanic's POV)?

Hello. I am looking towards a used 2009 corolla LE from a private party. The man owns a transmission shop and we checked his car there. It currently has a clear title, no accident carfax, and 37,000 miles. It was last serviced at a toyota dealership around 32,000 miles. BUT when we checked under the hood, I noticed there were 2 blue digits markings on top on the transmission. How do i know if the car's transmission was touched/tampered, you know. The digits were like hand written with "37" Is this normal or what? I know he owns a shop, so who know what happened on the down low without carfax/dealer knowing... but then again the mileage is 37,000, which is not bad and new.. the engine should not be acting up with that mileage.. your opinion? Thanks.