Please be careful when dealing with people you don't really know. There is a thread on common practices of scammers. If the person you are dealing with has just made a new forum account and is offering a crazy great deal, err on the side of caution as if you would in-game when a lvl 1 character is trying to sell you something.
Also remember to take lots of screenshots of the deal agreement and the deal taking place. If you get scammed, these could be helpful in getting your items and zeny back. I have had friends get scammed for all sort of things and the screenshots got their items back.
The following is the forum's policy on RMT taken from a post by Sloppy. If you choose to take part in RMT, then do so bearing full responsibility for whatever happens afterwards.
This forum is an unofficial forum, meaning it is player-made, and the developers of the game do not operate these forums.
Personally, I do not care if you want to buy or sell rubies or other items for real money.
However, there are several risks involved and I would like to point out the Real Money Trades Policy which is posted on the official knowledge base at warpportal:
NEOCYON / WarpPortal do not support real money trades, and it is against their rules. So if you decide to do real money trades, such as buying or selling rubies for real money, please be aware there is a risk involved - not only of being scammed, but also being caught by the developers of the game.
From what I have seen, warpportal does not really go out of their way to find ruby buyers/sellers, etc, so in reality the risk of being caught is very low. I recommend you use a different name on the forums than your in-game character name, and use private messages as much as possible - just to be safe. However there is always a risk of being scammed.
I recommend not doing real money trades unless you are fully aware of the consequences, and willing to take the risk.