I'm not sure what the answer to your question of how many "not there"'s it takes to remove a report, but fortunately, I think you'll find that at this point anyway, the vast majority of the Waze community is mature enough to pull stunts like that. And for the few who might get a thrill from it won't really negatively impact anyone else since racking up "thanks" points are just another form of imaginary internet points that don't really mean anything.