As the owner of several challenge caches, I find it tedious to verify the qualifications of people who claim finds. Sometimes they link to the Project-GC checkers, sometimes they don't. Even if they do, it's just text that they write in the log and could easily be faked (haven't seen this done yet, but it's possible).
It would be really nice if there was a tool on Project-GC that would show the challenge checker status for every user who has logged a find on my challenge caches and call specific attention to any logged finds that fail the challenge checker.
The user experience might be like this...
User loads the tool. Tool shows a list of all the user's owned challenge caches with a single-icon indicator showing the status of all the finds for each cache (green = all logged finds are valid qualifications, red = one or more of the finds are for users who do not qualify for the challenge). User clicks on one of the listed challenges. Tool shows a list of all users who have logged a find on that cache and an icon that shows their qualification status (green = challenge checker passes for that user on that challenge cache, red = challenge checker fails for that user on that challenge cache). The icon is a link to the challenge checker prefilled with the selected user. The list also links to each user's Geocaching profiles as well as the individual logs.
This could probably be a Project-GC premium member only feature.
This would let me as a challenge cache owner easily see at a glance if all finds are properly qualified or if there are any that I need to look into and perhaps contact the user and/or delete logs.
A related feature would be similar to the email notifications for FPs and log images. But this one would be a notification for any logged finds on your challenge caches for which the user does not qualify for the challenge.
Of course all of the above would only be possible for challenge caches for which a checker exists.