Strange custom in here...

I would like to share with you the strange custom, which I spotted, is taking place in here. It's about the buses. Here are the bus stops, but there is no timetable at all. Every bus and every bus driver is changing the number of the bus after he finishes the one round. So, if you are waiting at the end of the bus round, you are looking at the bus which number is e.g. 1. And then, when the bus driver is starting the engine, the number of the bus suddenly changes into 6. <wtf> you think :D But, unfortunately it's not all of its strangeness. You have to buy a ticket in the ticket machine just next to the stop. If you are lucky and you actually have bought the ticket you now can enter the bus. But... it's normal for this place that the bus driver tears the ticket... So, all customers are being checked by the bus driver, if they have a valid ticket. But... suddenly the bus stops, and a man enters and is checking if you have valid ticket... What for? Well, I was thinking a lot about that but surely I have no idea...

Maybe you have? I am waiting fos some ideas? 

Maybe the problem is not in the public transport in here, but in my Polish mind, which makes me think of the lack of necessity in this custom.

And... I have one idea... Maybe the bus driver is checking the customers. And maybe the inspector is checking the bus driver... Maybe...