I played around with the widely publicized Gold Cheat and came up with my own Compound Interest solution:

Let's say character A is the Pooled Gold Character and Characters B through F you can routinely change out in the Inn for $200 a pop. Do this several times for a net gain of $5000 to make this worth your while. Pool your gold one last time to Character A, then leave the Inn with at least Characters A & B in tow. Go to the Armory, click on Character B's portrait, pool the gold, then leave the Armory. Go back to the Inn, click on Character A's portrait, pool the gold, then click on Character B's portrait, remove the character, then click on their portrait to add them back.

If this is followed EXACTLY, you should have $5000 in both character's bags. From here, just follow the standard gold cheat of removing and re-adding your "money" character. If you accidentally click on the character's inventory detail page, you will lose the gold in your "money" character's bag and you will have to repeat the off-site pooling at the Armory in order for this to work again.

There's no need for the complexity.

Whenever my money is getting below 200k I do this. After selling items in the armory, so that each character has at least a few hundred gold on them, I go to the inn. (Idea here is that each character enters the inn with money in their pockets.) Then I pool gold on main character and remove all other members. I reinvite those members and pool gold on the main member again. BOOM! My money doubles. Sometimes you have to wait for the pool gold to show new numbers longer than others. From there, I can remove all members but leader again. Reinvite them and pool gold on leader again. My money doubles what the last count was, i.e. start with 150k to 300k to 450k etc. No need to go to the armory and back and forth or leave town. Though after done making the money I would leave town and save, as I don't trust the town.

Just my way for making money.