When you are at a high level (20 or more, the higher the level the more the money) make a new account (Free World).

On your high level account, put something in the chest. Then go to your extra game and take the item and sell it. Now on this extra account, buy as many health potions as possible (or until you're tired of going from town to town buying them. Because this is a level 1 game the potions are 4-5 gold (but when you’re a higher level they can be 100 or much more). Now put the potions in the chest, retrieve them on your high level account and sell them.

Note: if when you sell the potions they’re only 2 gold then put all potions into the chest and go buy health potions from a store. This should make it so you get more when you sell them. Also accessories that make the selling price more might help.