The bad guys already know these scams; So this will not educate any new scammers. As I always say Ignorance can be cured; stupidity is forever. This should give the honest players a leg up.

These are many common scams in these MMORPG games. The trade scam is common to all of them. I have broken the others into Impersonations and technical.

The trade scam
Trading in MMORPG games is usually secure and requires 2 steps:
1) first place your items for trade then hit confirm
2) when both parties contirm, trade can be initialed

You are shown a very valuable item and offer to trade for cash (cheap or a lower priced item). The trade is canceled!

Long wait

This continues until in frustration you hit trade complete; at this point (if you are lucky) they give you a cheap substitution) rule of thumb; trade fails 2 time there will be no third.
In many games this can happen because icons are reused for different items. Also the items that are plused also use the same icon but does not reveal the pluses until clicked. Any item that has a cheaper alternative can be used in this scam.
In Last Chaos pets are favorite for this scam. Knights Online reuses many weapon icons for different level weapons.

Promised delivery
you are offered something valuable but must pay first and delivery afterward. Item being offered are Purchased Items, Items in the Storekeeper or Bank and even player's accounts. Players are giving valuables to complete strangers with only the promise of an actual return. If you have lost your valuables don’t waste too much time waiting for delivery.

Impersonations.
It very important that you learn how to tell the authorized players and the Game employees from the normal players

Players
Similar names:
Recently we had a moonstone event where you give a moonstone to the GameMaster and you were entered into a lottery. There was a player standing in the town circle, where everyone teleported, with a similar name to the GameMaster accepting moonstones. If asked, she would admit she was not the GM but that still keep accepting stones from other players.

Trusted Clannie
Some players jump from clan to clan just to gain your confidence. As a guild friend they want to borrow your best equipment to take a picture; enable their other character to kill a monster, to finish a quest. Etc
This scam does not work on the victim’s greed but his civility. The victim is asked repeatly to lend his best items so the scammer can take a picture or any other reason. If the victim lends them the victim never sees them again and the scammer quits the clan and goes off to find a new clan and a new victim.

Similar names are also used by players to pretend that they are your friend. You may know Rodger but this guy is R0dger. Or you know XxSamxX but this is xXSamXx.

Only lend something that you will never miss if you never get it back.

The quest items Scam

Someone offers you an item and tells you that it does something special for your class (Experience etc) but doesn’t work for their class that why they will sell it to you. You will not find the NPC to who they send you and will call you stupid that you cant find them until you go away.

The Fake GM upgrade

The stooge shouts that the GM is upgrading all items 3 levels for free. Give him your best items. He keeps shouting "thank you GM"; "thank you GM". After the scammer inventories are full they disconnect. Some Games will do an event like this so if you wish to participate in the event make sure you know how to tell a real GM

Technical

Just read about the 999 999 999 scam.

You are approached by someone who says that they have a money hack! go into merchant mode and enter a valuable item with this price
999 999 999 spaces are important as commas will ruin the effect. Oddly cheap items don’t work. You have just sold the item for 999 coins. The game code stops at the first space.

Party Bug
You are in a party where the loot is distributed in a round robin method (each players gets the loot in turn. One of your party members asks if you heard about the Upgrade glitch? Answer negative and he will tell you to drop your weapon and armor then pick it up and they will be upgraded. If you are lucky, you will get one of your items back; the rest will be distributed among the party. In a 2 man party, you will be asked to drop your weapon, doesn’t take more than to 2 tries to give your weapon away.

Intimidation
You are approached by a players who claims to be one of the Games Employees or authorized volunteers . Give up your hunting area, weapon, armour or other item or he will ban you. This is bull. Take a SS and report them through the proper channels as an abuse of power.

In a similar vein, they may request your account id or password. Real employees do not need your password and volunteer have no business in your account.

Any player who demands anything from you because he is a member (or friend of a member) please take a SS of the conversation and report them through the proper channels. Even if he claims to be who he is; he will be punished.

There is some confusion between being scammed and being overcharged. A scam is always a broken promise but not all broken promises are scams. You may be overcharged but if you got what you paid for; it’s not a scam.

Strange that not one victim asked themselves why is this guy doing me such a big favor? Better to lose a good deal than buy a lot of regret.

I would hope that there would be no additional post to this topic but I know human nature. Remember if it seems too good to be true; it's not

Additional links:
Last Chaos official
trade scam variation
hacking and Keylogging
Based on my list of scams at http://forum.knightonlineworld.com/forum_en//index.php?showtopic=83405