The rules should be revised to prevent these and since scams aren't moderated, the forum will always lack security. Escrow is an option to be safe but newbies can easily be trapped if they use an unknown escrow another member recommends and cases have been reported here.
The main issue is that people here prefer buying stolen goods as the price is cheap (15% the face value) and when there are such customers, how can these good be avoided from being sold here?
Gambling too needs to be stopped and the ability to create multiple accounts which increases the chances of getting scammed. Moderators manually verifying accounts or having a newbie jail (which existed earlier) can be an option too.
Having a mobile verification feature is being considered by the forum admin but only for the new forum that's going to be launched and not for this forum. I guess the new forum will be much more safer than this one.
Multiple accounts is fine IMO. No one who is really trusted would be selling their account IMO. And if it happens, the password would definitely be changed and if the account starts being active after a period of inactiveness, members would rise a red flag. Gambling is allowed in certain countries and the forum isn't opening a gambling site so its alright.
The recent hack was caused by social engineering. No amount of protection could have 100% prevented this unless it is hosted by theymos himself.