Best Posts in Thread: giveaway threads

Is there a way that we can make it so when someone posts a giveaway thread, all the people post to enter, and then when it's over it's locked?
this way people stop bringing the thread back after it's over and there's nothing left.
Or can we have staff go in and lock any threads that are over yet people are still posting?
Either way.

 

I will go through them and lock the completed ones and try to go through them as they go

Completed!