I agree with Fieros.
If tour not selling desirable goods then you won't make any gil. I farm certain areas in the game for maybe an hour and make roughly 100k + and it usually all sells over night. Also I have 2 retainers set up. One with gear I've madee ( only. Leatherworking like 10) and its low level gear and I make good profit off of it. And the other with goods that sell fast from my farming.
Also putting your retainers in cities that have highest population helps also... I find my gear sells faster there.