On SA, we have a guideline that health and medical related questions (for example, is it better to eat green beans raw or cooked?) are off topic. However, many new posters don't read the FAQ and guidance; they just jump in with their questions.
I am sure there are analogous concerns at every site.
While no perfect solution is possible, I think we have an opportunity to catch some of these new posters before their questions are put on hold, and we loose good will.
I am suggesting that there be a filter applied to the title text and body of new questions when they are submitted, matching for keywords (or regexes, if that is reasonable). If the filter hits, an educational message would be displayed saying something similar to "Your question contains the word(s) XXXXX. Please be aware of our site's guidelines YYYYYYYYY" and give the poster three options: Return to editing, Cancel submission, Post Anyway.
Each site, via its moderators, should have several slots to set keywords or regexes, and the message that goes with them.
So here on SA, we might have one configured as something similar to:
Keywords health nutrition healthier nutrient Message: Health and nutrition questions are off topic at Seasoned Advise. Please see our FAQ (with link) for more details.