If I said "I baked a cake for my mother," then you could say "BUT YOU STOLE THE FLOUR!" It doesn't prove anything.
That said, there were contextual clues. If you go back, I said, "You get what you need through corruption..." The next reply was agreeing and expanding on that. This strongly suggests that each step in the description involves corruption in some way.
That said, hopefully you're now clear that these blat networks involve pervasive corruption.
When a community that is used to blat networks moves to a different country, the blat network doesn't go away. Throughout US history, it has been common to see blat networks in immigrant communities turn into straight up organized crime. The most famous example being the rise of the Mafia. But it is hardly an isolated example.
It was perfectly possible to have a decent salary but nothing to spend it on because the better items just aren't available. Maybe there's some delicacy you enjoy, or a special item you want like a cassette player and you could afford those if the store actually had them, but they don't. In that situation, your ability to buy more desirable items depended more on your connections or perseverance in doing things "the hard way" like queuing for hours to buy bananas, or recycling enough kilograms of paper to buy a book.
Yes. It's fascinating, HN is in most ways a bubble with a particular kind of leadership, but sometimes these cultural differences shine through.
To me, it's completely obvious that in the case of a plumber working through blat, he's not just legitimately doing extra work (assuming the law allows that in the first place). Of course it means the plumber is working on your pipes while he's supposed to be doing his actual job, or maybe he actually does it outside the hours but when he needs to replace some part for you, he steals it from his work. But apparently to people who grew up in a different environment, what comes to mind is legitimate side business.