Quote Originally Posted by Big D
You can get limitless Gil even easier by defeating a lot of Mesmerize monsters (weird unicorns with boomerang horns) and refining their horns into Mega-Potions with the L-Med-Rf ability, then selling them with Sell-High enabled. Takes a bit time, though.
Being able to retrieve missed GFs at the castle is handy, though I've never actually had to do it. I didn't miss any GFs the first time through (except for those you can get whenever you want, e.g. Tonberry and Bahamut); and besides, I could only find about half of the special monsters in the castle till I looked at a guide.
I used Carbuncle's Recov-Med Ref Trick to gain Gil. Believe me it was heck boring.