Newbie can't post at all, only can report junkers (Confirmed by mods first) on the forum to earn points so he/she can post something to ask or gain ranks.You can put some points or karma or something for it. And set the limit you must reach first so you can earn 1 post..
Example: Newbie can only read some section and only can report with certain range of time and gain 1 point if it get confirmed.
And a reported post going get some mark on it that it has been reported by who and awaiting for mods confirmation.
This would:
Discourage new users as all public forums allow you to post something from the start, even if it's only in a single section.
Give the staff a lot of additional work as a lot of these reports by newbies would be useless. You can't expect someone who just made an account to start accurately reporting others.
Encourage newbies to spam reports to get it over with and be able to start posting. If you report 100 posts some of them will be accurate, so why bother to even read them? If someone would get banned for report spamming it's not a big deal since the account was new.
Make high level accounts worth even more and trading flourish.