Can I get blacklisted for one bad send?

Possible But Context Matters. One exceptionally bad send (massive complaints, hitting many traps) can severely damage reputation. Normal bad sends typically cause gradual damage requiring multiple incidents.

The severity depends on what went wrong. Sending to a purchased list full of traps differs from one campaign with slightly elevated complaints.

Single incidents can blacklist, but usually extremely bad ones. More commonly, reputation damage accumulates over multiple problematic sends before reaching critical levels.