Well, my question is how do the government know we are holding crypto and how much we had if we are keeping our assets anonymously? Maybe they are getting personal information from the local exchanges because that is the only way they can control since local crypto exchanges are compliant to local SEC. But here in my country there is no clear regulation regarding taxation but maybe they'll have to implement it for the income tax I am not that sure.
There is a chance, that when persons submits an annual income tax return, his expenses does not much the amount he has spend, and it leads to a request to pass personal audit. For example when you earn $1000 per month, but buy a car that is worth $100k, it look suspicious. Or people have food store clients cards that give discounts. They a personal and through them it can be noticed that person spends a lot, and relate it to his earnings. Even a thrown away tv box can tell that a person has money. There are little nuances, little flags, little indicators everywhere that tells that persons spends more than earns. And next it will be a matter of time when a person on a freewill gives information about his crypto address.
If someone uses crypto to avoid tax. That person can do that only for a minor expenses. Cant hide car, house, land purchase by that. I dont know if there is such practice in your country, but in some European countries, when your purchase for more than 1000 EUR, you can might get asked to provide ID. Guess what it is done for ?