What you wrote above (colored in red and underlined by me for emphasis) means something different to me that is does to you. What you wrote above to me means that if we're still negotiating via PM, and someone else throws down the 'take it' in the thread, I lose. However, if you and I have agreed to a deal in a PM exchange, we are no longer negotiating - we have an agreed upon deal in place , and a thread 'take it' should not dominate that deal.
To accomplish what you are intending, you would need to say something like
" IN the Thread Trumps ANY and ALL PM activity, whether a deal has been reached, or not " , which would be a bad policy, in my opinion.
edit: beat me to the post, comix4fun