I think such a filter-tool will not give you an usable result:
- Basic members that found caches and get premium after some years, may not favor that caches afterwards.
- Premium members that make a pause (e.g. illness or nursing family members) will disappear by holding basic membership and reappear when getting back premium. Furthermore, when that specific cache is a few years old, it might got an favo by a premium member that now is (temporarily) a basic member. You have to take that into account.
- Premium members that focus on visiting "high quality" caches my have a long list of "to be favored caches" if they run out of favos (or even want to hold back a few for special cases). They will be shown on such an filter result and you may misunderstand the (current) unfavoured state.
Thats my opinion, your question may be understood critically. But of course I want to be constructive...
With following link you see the opposite of "who gave me no favorite" on your caches:
"Who loves my caches / Wer mag meine Caches"
Nevertheless your question is eligible - just an honorable reason is missing.
Maybe there is an option to filter all names of finders of one certain cache, from whitch you can remove the favoriters (list of favoriters is available on listing page)?
The determination of such cachers would of course also be of interest for other caches of competitions. I think your question is not goaling your caches. In Munich there was a competition with some 99,x % caches. Of course, there such an analysis is of interest for some people. But nevertheless, the above mentioned problems remain (basic /premium membership change, run out of favs, ...).
So your question is eligible (especially for competition caches) and I'm also interested in a solution.
I think the needed tool might be the following but with the possibility to give a cachename/-ID instead of an username: ForgottenFavorites