Scam

From the Dark RuneScape Wiki - follow the rules, or else!

A scam is an unfair (usually deceptive) method to trick another player out of items and/or cash. Scams often target valuable items or large amounts of coins. Scamming is discouraged, as players who are found guilty by Jagex may receive a temporary or permanent ban or mute for breaking Rule 2 and/or Rule 3.

Luring is also a form of scamming reportable by Rule 2 and can also lead to banning.

Each time in a trade an item is removed or its quantity changed, a red exclamation mark and line appears at the spot of the edited item.

Jagex has added an update that does not allow players to make too much profit from a trade, especially during a scam; the amount of profit allowed varies according to the amount of quest points you have. This effectively prevents people from being scammed. The table for the amount of monetary disparity allowed is shown below.

Quest points	Margin
0 to 10	5,000
34	10,000
75	18,750
150	34,615
225	50,480
270	60,000

For more information on this update, see the development diary article on www.runescape.com.