Mess when displaying text saved in tinymce. How to help the end user?

Question

TinyMCE

The question is dictated by the fact that we often have to deal with requests from end users to "correct text and photos on the site." You start to find out, it turns out that the user simply copied the text from some site, pasted it into Word, made changes, formatted it, inserted a photo.
Copied all of this and pasted into various variations of tinymce-like plugins and saved.
What are html tags - the user does not know. Open source and edit there - "why do I pay money to the support service then?" Well, you understand ...
How do you treat this? I already thought about writing a tag handler to remove something or replace it with something ...
But maybe there are other, simpler options?