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How do people buy properties with crypto without triggering taxman and anti money laundering stuff?

Which ones?
Many African countries also support it. You have to find a trusted real estate agent.
With emphasis on "trusted" ;). Its easier than you think as some of these guys are very rich and barely care about a measly 50k. But it can go the other way and you will lose everything and get robbed.

Cash transactions are the norm anyway due to non working alternatives.
 
Excuse me for asking but is this a serious or joke answer?

Proving one owns a crypto wallet is sufficient proof of funds? One signs a message from a crypto address and that's sufficient?
YES!!!!
They will ask you to make a few small transactions. When they have done so you will be confirmed.