BCH SLP Token Swap Trade App

https://bchpool.github.io/

Trustless solution, can sign offline, low 0.75% swap fee.

Users can stake any token or BCH and set their own profit margins.

I have never visited said dark web market... But i guess you'd either have to buy a pre-written market script, or write one yourself...
You'd probably have to run daemons for each coin you wanted to accept, and use the daemon's json-rpc interface to create deposit addresses and handle withdrawals.

Not easy stuff... Difficult to get running in the first place, even more difficult not to get caught by law enforcement.

Don't run illegal markets, it's not worth it in the long run... If you make even a single slipup, you'll end up in jail...