I've done plenty of trades with people I don't know. If you keep a few rules in mind you never get scammed:
1. Never borrow stuff or share account info.
2. Always double(I triple check) check everything you trade, including the stats of the items in trade and the amount of coins/rps involved
3. NEVER accept offers which seem to good to be true and require you to either pay up first, basically anything that doesn't involve either (instant)EM actions or the (instant)ingame trade mechanism
4. When buying from chars that sit shop CHECK every price manually before you buy it, some people alter the price so it looks cheap in F or they put an item with another 0 added to the price
5. Don't use any other currencys besides RPS/ECASH/Crone/Items
6. Don't be greedy and buy an item ''cheap'' because you just got a PM another person needs that item, you think you'll make money as middle man but as soon as you bought the item the second buyer is gone
7. Don't login into keygens or whatever, get a proper virus scanner and don't reply on people saying they are giving out free stuff via mail/Facebook/rohan EM or ingame etc.
9. In general don't be a fu*king retard, don't be greedy and use your brain
Playing for 7 years and haven't been scammed once, I don't understand why so many people have issues with this, or maybe I do, human greed or stupidity.