You must have never done anything like -say- use the 38 to connect to CalTrain shortly before or shortly after rush hour. :)

I made the 38->30/45->CalTrain or 47->CalTrain ride every single day for nearly a year. It seemed like once a month or once every other month, MTA fare inspectors would board the 38, 47, or -far more rarely- 30/45 I was riding and check everyone's proof of payment. On the 38 and the 47, it always took about five minutes and was a... fairly irritating delay on top of a really irritating commute.