I'm not complaining, but just saying that although plagiarism is a ban-able offense here, it shouldn't be on the "top" of your priority to actively look for them just for the sake of it.
I think your reasons cannot be forced, why you forbid people to do what I think is good, to reduce plagiarism.
and how they can get a reputation for posting plagiarism.
Lastly you say it doesn't have to be her/his top priority, in my opinion it doesn't matter as long as she/he does it right,and make the forum better.