The gem trader runs the Gem Trader stall in Al Kharid. He buys and sells sapphires, emeralds, rubies, and diamonds and their uncut versions as well. He has no main stock; he only resells jewels that other players have previously sold to him. His shop isn't frequently used due to the predominance of the Grand Exchange, where sellers can receive more money for the gems, cut or uncut. In the Family Crest quest, he directs the player to Avan at the Al Kharid mining site.
Prior to the release of the Grand Exchange, it was common for the gem trader to have a fairly full stock on free-to-play worlds as his shop was the easiest way for newer players to sell their gems. Newer players were also able to make small profits by buying uncut gems from the gem trader, cutting them, then selling back for a higher price.