That option has been discussed and dismissed - I personally think it would create more problems than it would solve. If you were a new and as yet unregistered user, or a prospective buyer, having to wait for your post to appear and then for an answer, perhaps several days (mods are unpaid and do it in their own time), then you could get discouraged.
Because we are a small niche market the forum does not get anywhere near the spam posts of other forums so they are not really a serious problem - and long may it stay that way.
EDIT: To give an example - the SPAM post which (probably) started this thread is still there 5hrs later waiting to be removed. I did post a spam report to the Mods within minutes of it appearing but different date/time zones, a life outside of monitoring these forums, etc means that the mods cannot always respond instantly. If I was a new or prospective user waiting for an answer to an important question and my question has not even appeared after 5 hours then I would probably go elsewhere.