Well i've noticed in the giveaway section that even after the giveaways are over, people still post saying:
"Hey i want one"
or
"Me please"
and then a spam fest starts.
So i thought why not give the thread creators limited moderation rights for their own threads ONLY in the GA section so that they can close the thread when they're done with it or open it back when they want to restart it.
This should reduce spam in the section.
Hope this helps =D