In this game quests don't provide much gil, they're mostly for story progression or unlocking jobs, etc. Most players gil comes from farming (killing mobs and selling the drops on the Auction House), or crafting.
First be sure to get signet from your gate guard every time you go out, that way you'll get crystals when mobs die. A stack of crystals sell for 1-4k (depending on server and type of crystal). Other good things to sell are stacks of silk thread from crawlers (20k), honey (5k) and beehive chips (10k) from bees/wasps, landcrab meat sells well to npc's (don't sell a stack for under 4k on the AH).
Once quest you can do is Mihgo's Amigo
, it only pays 200 gil for 4 Yagudo Necklaces, but if you want to level ninja you'll need the fame this quest gives so you can get utsusemi: ichi
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to see what things are worth selling on the AH, be sure to select your server from the drop list first though. Edited, Jun 30th 2012 5:10pm by Zijder