From the admin side, we see the following
- lots of accounts trying to register with the same LLM generated text, or nonsensical spam in the registration application. Those get blocked
- some accounts that immediately make it obvious that they are a spam bot by posting unrelated advertise-y content as their first post. Those get banned quickly, and usually the home instance prunes the account within a day
The recent "DM me" spammers and the accounts that post on !selfhosted@lemmy.world are a good example of the second category.
It's pretty rare for a bot to be active for much longer than that. Usually some eagle eyed user will spot it and report it up the chain.