This is false... your cryptos aren't 100% secure and they can be robbed. Let's say you have your private keys on your home in a paper wallet, and a thief joins to your house and steals those private keys, another example is, let's say you have your private keys in your computer, and you download some software with a malware, that way your keys can get rob. And a last example, let's say you work hard on security and no one can access to your private keys, but sadly a user finds your private key with brute force.

You can do this but would be done in an illegal way, because the government loves taxes, and if you close a deal without paying taxes then you will be doing something illegal for them.