If you're exchanging cash, you still theoretically have the legal obligation to declare it. Businesses accepting cash have the obligation of issuing a receipt, and you may have some obligations of keeping that receipt.
Now, it's true that these things are hard to enforce, or even impossible for small enough sums. But people systematically flaunting the rules for large sums of money will get arrested, even with cash.
> If you're exchanging cash, you still theoretically have the legal obligation to declare it. Businesses accepting cash have the obligation of issuing a receipt, and you may have some obligations of keeping that receipt.
I'm pretty sure that's legally required even when buying with crypto
Now, it's true that these things are hard to enforce, or even impossible for small enough sums. But people systematically flaunting the rules for large sums of money will get arrested, even with cash.