What do you mean by black market? I am a registered user of more than a dozen exchanges, although I haven't used any of them for almost three years. On the other hand, it is relatively easy for me to convert my cryptocurrency to fiat using a P2P platform (which doesn't have any privacy requirement). And even for mainstream exchanges, their KYC process is not very strict. I know a few guys who are using exchange accounts that are registered in the name of others. Also, KYC documents are easily available in the dark market and you can use them to set up a fake exchange account.