You’re obviously using Tor, which is anonymous without doubt but isn’t anonymous-enough.
To be truly and completely untraceable, you need to first make sure you don’t leave any loopholes from your end.
For e.g. never use a username which can be linked back to you in any way, not the name of your pet, your neighborhood, your crush or anything else. Even your password should be as random as possible.
Then, make sure you use a VPN while accessing Dream Market in addition to Tor browser. Without a VPN, Tor can still be hacked and traced, with a VPN that literally becomes next to impossible to do so.
Third, always use third-party PGP encryption (such as GPG4WIN / Kleopatra) to encrypt your messages and communications on the marketplace and avoid using the inbuilt “encrypt message” checkbox.