OK here is how you get easy gil:
1) Have a main character and a new character
2) Start a new character
3) When you are given the adventure cupon give it to the person that gives you 50G for it
4) Go up to the guy at any AH that will transport the gil to another character
5) Then type in the name of your other character and put the 50G in the place where the gil goes
6) After doing all that repeat the process and you will have free gil
Sell 12x Crystals for gil at Auction Houses. You need to be wearing a signet for monsters to be able to drop crystals so make sure you have one first.
Kill goblins and sell their armor, you can make 250 - 500 gil each.
OK if you want to make LOTS of Gil you can do it the easy way or the hard way. The easy way is to lvl your THF to lvl 15 or 45 (45 if your really board) and go to Bastok and farm BHC (Beehive Chips) off of Zegham hill. The hard way is if you don't have a THF at lvl 15 or 45 (at lvl 45 you get TH2(treasure hunter 2)). The BHC's sell for 10-15k from what i remember. And if you want to ask me about this or want some help farming (i can only help you if your on diablos server) ask for spiky, xana, hyia or uzkay (these are my chars) or if you have any questions email me.