What is the recommended strategy if posts are being poorly edited? Especially if a single editor is editing many posts and many of the edits are problematic?
This isn't vandalism. Most edits improve the posts in some ways, but they frequently also include edits which are at best unnecessary and at worst positively harmful.
I just partially undid an edit which included changing correct markup for a document element into incorrect markup. The code was definitely better prior to the edit. (I copy-pasted the original code back.)
Earlier, I restored text which was not strictly needed in the post but was an attempt to respond by the OP to suggestions in the comments on how to improve the question. Although the OP had misunderstood what was being requested, simply removing their attempt at improvement seemed problematic. Moreover, the text did help make a little more sense of the question, at least in the sense of understanding what the OP was trying to do in a broad sense.
I can't respond to the editor in comments because editing a question doesn't mean you can be pinged, and the editor is not leaving comments (at least on the questions I've been re-editing).
I can't, as far as I know, offer to chat with an editor for the same reason. Nor can I flag an edit for moderator attention.