Sounds more like social security avoidance, or general taxation avoidance.
Which country will take 30% cut from incoming foreign transaction? The highest combined fees I could find are for Sub-Saharan Africa and those are below 10%, supporting tax/social evasion claim.
Could be completely legal but when folks don't provide details its often safe to assume the worse scenario when it comes to money, taxation and screwing the government.
I believe some countries e.g. Cuba have different "official" vs "black market" exchange rates. A 30% difference wouldn't surprise me.
What they are often talking about there is countries where the official exchange rate is very different from a real world exchange rate: This happened in Argentina quite often. That led to special black market stores where people would give you local currency for dollars at better rates, and often also had some crypto support. You are then going past the legal market either way.