Easy Fol
There are only a few ways to gain Fol easily, as if it's not easy enough to obtain especially late in the game. If you have some high value items such as Shield of the Arc or the Sword of Marvels you can replicate them and use Group Appraising to sell them for quite a hefty amount of Fol.
In the early game you can pump skill points in to Purity to gain some quick and easy Fol. You can also buy cooking ingredients and cook them, reselling them for profit but it does take some time to really accumulate the Fol this way.