Currently, those who regularly trade cryptocurrencies do not use intermediary platforms such as visas, mastercards to trade, they will trade on the black market and have a cheaper price.
I don't know anyone who is using the black market to buy Bitcoin. I think what you are referring to is the peer to peer OTC market, which has been gaining a whole lot of popularity in the last couple of years.
There is so much more liquidity in the OTC market that whales no longer have to lose a percentage by market selling due to slippage, and payment options can vary as transactions could be settled in cash or digitally.