You have to be at the fallen village. Purchase like 50 bottles from the food store, walk all the way to the left. Fill all the bottles in the well. Sell your elixirs for 37 gold. (over 10 times the amount you paid for).
So basically, you buy a bunch of 2(purchasing unit) bottles, fill 'em with potions of healing, and then you selling for maximum profit. It might be a reference to the herb-grind of the first sinjid, as trying said. I remember spamming it, then looking at the moon.