Merchants Quests are available in each city at the Merchant Guild Master. If you don't see a quest, it's because your skills levels are not high enough. The first time, you have to subscribe to that guild. Then you will be able to see different quests in the different cities. Higher level quests mean you earn more money and experience (usually). You should start your Merchant Quest in Alexander or Athens (Beirut or Istanbul are fine too). Those towns will ask you to do simple quests like run to the trader and come back. It's a way to start making quick money. After you start to get use to it you can attack the bigger quests. Look at the list bellow to see all the quests.