I would also think that if you were to monitor the number of pages worth of posts a user has this would be easy to detect from a non-moderator point of view. For example a script could check to see that UID 41911 (aka BadBear) has 162 pages of posts as of 12 Jan 2015, then if their post count went up by 100 posts in the following week then they should have exactly 167 pages of posts. If they do have as many pages then payment could be made automatically, if they do not then it would be an "exception" where posts could be counted manually
Wouldn't there be a big margin of error if you used pages to check for deleted posts though? That system might work for many deleted posts, but one, two, or even ten deleted posts might not show up if you checked the number of pages.
For example, if their post count went up by 115, you would expect to see 6 more pages. But if they had deleted 10 posts, it would still be 6 more pages. It's only once they delete 15 or more posts that the number of pages changes (to 5).
There would be a margin of error of 19 posts per user per week. For hero members (under previous rates) it would work out to .0228 per user, and for senior members it would work out to .02 per user (also under previous rates). The margin of error would decrease substantially over time as it would become obvious that a user is exploiting this as their long term post page count is not rising quickly enough according to their post count increase.
There is no real reason to be deleting even 10 posts in a month (with a potential exception being sales threads, but even then you could increase that to 20 posts) so it would become obvious when someone is deleting this many posts and Stunna's position on default trust list would allow him to give negative trust to anyone clearly exploiting this exploit (which would be valid because they would essentially be scamming him).
The value lost from receiving the negative trust would greatly outweigh the potential gain from manipulating the system so people would have incentives to not do so
edit: people could potentially self report how many posts they deleted (approximately) in the last week so Stunna could adjust payouts manually for such deletions.
He could also check the
modlog which would show how many posts were deleted by a moderator which would also give him a good idea when it is time to ban a user from his campaign