The Rune to Adamant Scam is a scam in which the scammer pretends to sell Rune items which are actually Adamant. It is a form of item scamming, and is against Rule 2 of the Rules of Conduct. Jagex will give bans to players reported for using this scam. The scammer will bring several pieces of Adamant armour and/or the same armour or weapon types in Rune while advertising to sell the Rune items. Eventually, a player will trade with the scammer. The scammer trades this person and puts up the rune item, and the buyer puts up the money, the scammer declines and says "oops". They trade again, only this time the scammer puts up a the Adamant item if it is noted version of the same item (e.g. an Adamant full helm, instead of a Rune full helm). The buyer accepts without checking the trade screen. The buyer has just been scammed.
Always check the second trade screen to make sure that you are buying the item you want.
Iron may also be used.