You mentioned teachers and professors. While their salaries are very low, every parent is expected to gift the teacher money each year as a standard rule to thank the teacher. Then you have the 25% corruption (my figures were 30% of GDP) . For little Vova to pass his exams also required a contribution and if little Vova was not so academically gifted, the contribution would be more.

I had a friend who was an architect who decided to switch to law. After years of study all she had to do was pay substantial donation to the teacher and school and they would give her her law degree. Even though they had had lessons on ethics and corruption. She refused to pay and never became a lawyer.

Where I lived there was this grand estate at the edge of town, with blocks of land selling for $100,000 USD and people putting $750,000 houses on them, some even with minarets. These were huge homes, probably costing $5 million if built in the West. Two things were funny about this area. One was the road was never built as someone ran off with the money so you had luxury cars navigating a dirty road with potholes you could park a truck in. The second thing was the neighbour to my friend with the grandest house on the street. The neighbour's profession? A professor at the University. Knowing the salary, the neighbour was a masterclass in how corruption pays.