SaGa Frontier has a two-part infinite money exploit.
1) The Junkyard exploit: buy three pulls from the Junkyard in Scrap. Get your three things, talk to the vendor again, go to "Sell" and press the button to "sell" a Hyperion Bazooka twice. It doesn't matter if you don't have it. Do not sell an actual Hyperion Bazooka. If you have a Hyperion Bazooka, "sell" something of lesser value on the list twice.
Go back into the junk yard and pick up 7 more items. Repeat and the gear will get better. Once you have a sufficient amount of gear for your future party (the best common gun in the game is in there, for example), max out your Swords. Swords are one of the few items you can sell in Shrike, while some leather goods can be sold in Koorong.
2) Gold Trading: buy 5 gold ingots, one at a time, from Koorong. Then hop on a ship to OWMI, followed by going to Nelson. Nelson sells gold bars for 500 a piece, while Koorong's price fluctuates. Sell gold bars in Koorong until they go back down to 500, then go back to Nelson and repeat the process. Use as needed
2a) Stack Overflow: if you have enough gold bars to drop the price to zero, you can keep holding down well past it looking like you would sell for nothing. When you start scrolling back up, the sell price will start rising immediately, thus boosting the price artificially
if you play SaGa Frontier, I recommend these options. SaGa games have a reputation for difficulty to begin with and it's economy is broken anyway. You'll still wipe plenty if you don't know what you're doing. Besides, it's single player so who cares?