Q:

What to do with a user who's offering bad advice, and why are comments being deleted? 

It started this morning, with this question.  Yet another PHP "something's wrong with my string encoding, json_encode produces weird characters" question.  I closed it as duplicate of a question which explains the whole non-issue.  User haunts me complaining about abuse (now deleted).  User pouts in the comments to his question (now deleted).  User deletes his question entirely. 
Now he's back with a new question; same topic, but apparently he has understood the (non-)issue and wants to offer a solution to it nonetheless.  Fine, the new question is well written, on topic, not duplicated (as far as I know) and he's offering a self-coded "solution" as answer.  Great.  Except, the solution is wrong.  It breaks easily. 
I try to point that out in a comment.  Shortly after the comment vanishes.  I post it again.  Comment vanishes again.  Quite apparently the user is unhappy with me and knows of the flag button, and someone is obliging. 
So now we have this pretty highly rated question standing there with a pretty highly rated answer which provides a solution which you just know will break someone's production code half a year down the line and the user doesn't want to hear of it.  What do we do? 

A:

As has been indicated in the comments, not all removed comments are done so by moderators.  If a comment contains specific words (obscenities, certain commonly abused phrases, etc.),  a single "rude or offensive" flag can remove those immediately.  Also, if enough members of the community get together to flag a comment, it can also be removed automatically. 
In this case, your comments were removed by a series of flags cast against them.  The circumstances around this are incredibly suspicious, and these comments should not have been removed.  This is one of those things that falls into the category of "odd enough for a moderator to look into", so I highly recommend casting an "other" flag on one of the posts and explaining what you see. 
Coordinated flags against posts was once considered more of a theoretical exploit than a practical one, but we've had a small handful of users attempt this using sock puppets over the last couple of years.  We generally don't take kindly to this, and really appreciate when people point it out.  I should say that it is still extremely rare, though.