This scam puts up multiple items, more than what the buyer was asking for, and at the last second, uses something like a sniping program to remove what the buyer was asking for. This makes so that the buyer is left with useless junk. You can report this via Rule 2.
Person 1:Selling a rune platebody!
Person 2 Trades and puts up 55,000 coins and some other junk.
Person 1 Puts up the rune platebody.
Person 2 Removes the money at the last second, and hopes that Person 1 doesn't notice.
Person 2 Teleports/logs out.
Person 1 was scammed and Person 2 gets the money.
The origins of the Multiple Item scam are near the beginning of the game, around the time when junk trades were introduced. The trade itself, like many aspects of RuneScape, developed after the community of runescape developed in size and in time, so victims would not be tracable back through a small community and hunted down in a pre wilderness era. The scam was made extinct by a new message that appears when a trade item is changed