Scamming in Lineage II is not against the rules, as long as it's IN-GAME. You can scam someone for their armor, but not their credit card, for example. Here are a list of the most common scams in the game. Sure it may teach some people bad tricks but I think it's far more important to know about them, to avoid them, than to not know. Scammers are very clever people.
This one can be done with any of the crystals but I see it on D the most. Notice how they are assuming you don't notice that the PRICE and AMOUNT are reversed. Works with ancient adena too, anything usually sold in big amounts.
Craft Shop Scam
This is usually done with the lower level crafts, silver mold, VOP, stuff like that. The title will say something like 10a craft, 1-4 crafts, etc but each craft will cost 100,000 or 1,00,000. It looks dead obvious but when there's only one shop in Giran making something you need to craft a weapon you don't always pay good attention.
Bow shaft scam
The popular one is for bow shafts because the top bow shafts are worth quite a bit of money. And the fact that bow shafts look EXACTLY LIKE STEMS doesn't help anything. Old school people might recall the infamous dark screamer/doom dagger scam, which was just another scam where you try to pass off a low level similar icon-d item as a much more expensive version.
The noob SS shots look almost exactly like the A grade ones, so people try to sell the no grade ones as a-ss. Here's a picture of the scam and a shot from a real shop.
I've had this tried on me 3 times so far but this is my best example. I'm sitting right by Stiltzz, and someone pm's me with the name Stlltzz. You can see the real Stiltzz talking in ally chat, and I have him targeted. Usually the person doing this says the EXACT SAME THING as in this picture. That should be the first tip off, I mean how many of your friends talk like such a goof anyway? Usually if you try to target the faker person, they aren't even in town, but their alt, who will normally be a low level nobody with a weird name, trying to get your weapon is.
Soul Ore/A Crystal Scam
I couldn't find anyone actually doing this but I know it has been done. I set up shop to show the example. The shop title is A crystals but I'm selling soul ore. I put them side by side, see how very similar they are? This is the same as the other similar icon shop scams.
Some other scams are so stupidly elaborate I can't even screenie it.
One involves items that have the same icon, like the BOP shaft and a stem. Someone starts a trade with a BoP shaft, you see it, they cancel the trade. They say oops, do it again, put in a stem instead, and you lose a lot of money. I hate hate hate trade windows and always tell people to make a shop. This one assumes you won't check the item the second or third time the window gets cancelled and just accept it. Always check!!
Another almost no one does, because it takes too much effort but it's worked before. You yell that you want say, a DC robe. Scammer1 says they have one but they want you to buy X item for them and you can then trade it for the robe. Scammer2 has X item for 5 mill, you think woot I'll get a DC robe cheap, you buy it, try to get scammer1 to trade you the robe, only to find out X item is worth like 50 cents. Scammer1 logs out off the face of the earth.
The second one assumes you don't know what the X item is worth to begin with, and don't mind running errands for some random person you don't know. Everytime I think this is the stupidest scam ever, I heard someone falls for it.
Another one people like to do is ask a person, while in party, if their weapon/armor/shield looks a certain way when dropped on the ground. They even act trustful and say they will stand far enough away that if you drop it, there's no chance they'll pick it up before you. The trouble with that one is the party drop settings are usually on random or by-turn, which means very likely even if the item owner picks it up, it'll go to the other persons inventory.
I don't think this last one I can think of occurs any more, but people would claim to be able to enchant a weapon or armor for free, if they could just hold the item for a minute. If you hand it over, you never see it again. This is one of those types of scams that works in real life, since it triggers greed in the owner of the item and makes them willing to go along with it for profit.
An infamous scam is the A and S gem scam. People will list Red Gems (Which you get from a quest, and loads of them none the less) as A gems and charge about 20-30% cheaper than the normal A gem price. Because when you highlight them real quick, and the word gem is in it, you quickly buy a mass load thinking you got a steal, and you find worthless red gems in your inventory.
People do the same thing with S gems, but instead they'll be a low level accesory gemstone or Entrance to Sepulcher passes.
Red Crystal Scam
This ones a pretty bad scam as well. Currently Red crystals don't show up as an icon. So what people will do is list create a Package shop, claim to be a really really cheap shop. List everything really cheap, and then put a Red crystal level 8-10 in the shop for 100+m.
Normally you can catch this, but if you're too busy trying to rush buy the item, you could find yourself paying alot more than you had bargained for.