You may have met a troll (intentional or not). Don't worry, the Stack's got you covered.
This is actually really easy: you do nothing. Nothing different to normal, that is. All the habits you've developed interacting with good-faith users are going to fix this problem, too.
If someone's truly acting in bad faith, keeping to your usual behaviour will make ...
The best and simplest thing that the community can do is downvote bad answers. It's simple and intuitive, but has more power than is immediately apparent:
A user who consistently gets downvoted, and the majority of whose posts have a negative score, will be ...
A few things happen:
They get downvoted a lot.
Their material might be irredeemably low quality and deleted, or the answerer might delete it themselves. The rest sits around, accumulating downvotes, or serving as an equivalent of skulls on the ramparts letting people know what kind of quality doesn't fly.
Eventually, they will probably get answer banned, ...
It's possible to get at this kind of information with StackExchange Data Explorer.
When users sign up, how many of them come back?
This query computes the proportion of users active in the last 365 days who logged back into the site at least 7 days after they created their account for the first time. It turns out that, as of this posting:
80.0% of users ...
Note the date. There was a time way back that user names were not anonymized on deletion. That looks to have been added sometime post this user being deleted.
Relevant stack meta Why is this non-anonymous username on this non-migrated question greyed out and not a link?
Sure! So, we're not free to share the specifics of the diamond moderator version of the site analytics with the public. And beyond that, we don't have a specific "bounce rate" metric.
What I can say is that there's a healthy growth in new user rate, which is at an all time high over the last three months. There was a significant lull last Sept/Oct but ...
Normally quality doesn't require moderator intervention. As users respond to the low quality content by downvoting, voting to close, and voting to delete where applicable the system will flag that person as trouble and limit or block their access to the site, both answers above describe this well.
In extreme cases the moderators may contact users ...