Next, we go to how you get into said exchange. For local cryptos, You have to go through clearnet but you should still use tor. If you are using localmonero, Do the standard OPSEC shit.
Finally, We have the methods in which to get monero. If you already have crypto, Great! Exchange it into monero, back to the original, and then back to monero. If you do not then let us continue.
There are a couple of ways for each set of the person. For carders and fraud people. You can purchase gift cards and exchange them that way, or for people who work the streets, /d/murderhomelesspeople is a great sub. But before I get carried away, drug dealers should probably use cash in the mail. I have never done cash in the mail, but just follow the instructions from the vendors and you should be fine.
Never use a credit card, PayPal, bank account anything connected to you. Never log in through the clearnet, use an email specifically for crypto as when you log in you will get a request for an email.