Back in the day, if I saw some braindead karma farming post on Reddit, I took a look at their post history and quite a few times it was a brand new account. I would simply reply “Welcome to Reddit! How has your first [week/day/hour] been?”. I think precisely twice it turned out to be a new human user, the rest of the time they would just delete the comment (or possibly even the account).
Alternatively, they spend so much of their time listening to bots on the Internet that only other bots make sense to them.