How do you stop users from reposting same thread everyday?

[6piston]

here's the scenario i'm facing:

-Forums (classifieds section)
-Vbadvanced side column forums wide - latest classifieds threads module

Okay,
-Newbie sellers repost duplicate threads daily not knowing thread had been piled up by new posts
-Greedy sellers repost duplicate threads to gain advantage from Side Column Latest 10 threads from the classifieds

Moderators misses threads like these

How should i overcome this assuming moderators weren't an issue

is there a plugin out there to prevent repost within certain days?

thanks!!