Hi,
The best way to boost the relevancy is by switching to the index table engine and enabling it. That creates a custom database with occurence counts. That alone makes a huge difference.
How to NOT show a result for a single mention of the search term in page content?
That is not possible, as it’s still considered a match. You can however make the search keyword logic more strict to only allow full keyword matches. I suggest starting with only a primary logic “AND with exact keyword matches” and no secondary logic. If the results are too strict, then switchin to the “AND” as secondary logic will allow a bit more “lighter” matches after the exact keyword matches.
You don’t define your terms in documenation. What does “terms” mean in https://documentation.ajaxsearchpro.com/relevance-options?
In that case it means taxonomy terms – categories, tags and other taxonomy term matches.