Maybe in the "Headline" for the thread, the Seller should add SOLD to the title.

Pre-sale----- "Stock 2.5 T-Maxx for sale"
After sale---- "Stock 2.5 T-Maxx------SOLD"

This way, it eliminates people reading through a whole thread to find out it is sold, but leaves it open for other people to see that the Seller/Buyer are OK to deal with.....

Just a thought