The Dragon helmet scam was a scam in which the scammer would pretend to be selling a Dragon helm (formerly called Dragon medium helm), but quickly switch it with an uncut ruby in the trade window. This scam directly violated the 'Scamming' rule under Honour, and the punishment for those involved was typically a temporary mute or ban. The scammer would offer a Dragon helm to a victim, then switch it with an uncut ruby as the victim accepted to try and scam the victim out of their money. This scam was dangerous to careless players due to the visual similarity between the two items which can trick players who don't look carefully at the trade screen.
This scam became obsolete for some time when free trade was removed from the game in 2007. It resurfaced in February 2011 when free trade was reinstated, but since more powerful helmets such as the Dragon full helm were added before then, the value of the Dragon medium helm drastically fell to less than 50,000 coins. This in turn reduced the frequency of the scam. It is now completely obsolete due to the graphical improvements of ingame armour launched on 6 March 2012, which made the helm look significantly different from an uncut ruby.
Scammer: Selling d med 40k! The victim trades with the scammer, and offers 50,000 coins. The scammer offers a Dragon helm, then quickly takes it out and offers an uncut ruby before the victim accepts. The scammer accepts, and the players quickly go through the second trade screen. The victim has been scammed, and may now report the scammer for scamming.
This was an alternative method that scammers would occasionally use to bypass warnings given on the trade screen.
Scammer: Selling Dmed 50K! Victim offers a trade with the scammer. The victim offers 50,000 coins and the scammer puts in a Dragon helm. The scammer purposely clicks Decline and says "Oops..." to make it look like an accident. The scammer now offers another trade, inserting an uncut ruby, and hoping the victim doesn't notice. The victim puts in 50,000 coins and both players click accept. The victim has been scammed, and may now report the scammer for scamming.