Note to sellers: Learn your market. These arnt the easiest to farm so take the time to know who your selling to.
The main two buyers are Hate reseters (single) and goldsmithing crafters (stack).
Supply and demand for price is not always effecient with this type of product. GS will use this to skill on, makeing gold ingots. It takes four stacks of coins for a single stack on ingots. If the price of the coins total is equal to the selling price (or less) of the ingots, the crafters will by these in massive quanities. If their going to lose gill on it, most simply will not buy them. They will wait till they drop or look for something entirly diffrent. So that 1 or 2k extra a stack can make a BIG diffrence in selling quanity/speed.
Generaly, take a stack of gold ingots divided by 4, and thats your MAX selling. If you have a heart you may want to do a single 1k/stack less, to help crafters worried about losing items in a failed synth.
Divide the price of a gold ingot by 4 and never sell a single coin for less than that mark, they sell very fast as people need them for skilling up and for the tonberry hate resetting quest.