Problem is Sneezy..... The more sub-forums you create, the more threads, the more threads the more posts, the more posts you have the bigger the database and forum become, which in turn makes the bandwidth required more.....
To run a forum this size the owners are probably already paying close to $800-1000 per month to have it hosted and the required bandwidth. This doesnt count the manhours to set this up, plus all the moderators time in moderating each individual thread. If everyone just stuck with the original single thread and PM the seller this wouldnt be a problem... I dont see the need for a subforum, why not use the general forsale section in the main forum if you want to have an individual thread? We all go there.... if its for SA only.. mark in the heading SA Only, all the people from SA regularly go there.... so its really no big deal.....
If you want to get the forums bigger, I challenge you to make a regular donation to Skylines Australia..... if you dont want to do that, then quit complaining and abide by the rules set down by those in power.