Nintendo was late to dip their toes into f2p game economies and it shows with the poorly balanced bell economy in (farmville-like) Animal Crossing.
Turnips are a terrible way to make bells in the single-player game. You have to buy a stack of them for around 10,000 bells and then wait all week for the market to pop. Let's say you see it pop to 130-160, which is a fairly common range in my experience. For all the hassle of buying and storing turnips (AC's inventory management is high effort and turnips have additional restrictions) you might net 6,000 bells per inventory space. Thing is, Animal Crossing regularly generates bugs and insects which sell for 2,000-8,000 bells. They are also one inventory space, and they are available all the time with no expiration or holding strategy needed. There are also abundant resources like iron ore, where a crafted stack of 30 ore in one inventory space will net you 22,500 bells in profit. Turnips are low value per inventory slot.
To get around this, players coordinated online. Sometimes turnips hit a jackpot price in the 300-600 bell range. So that stack is suddenly worth 60,000 and now we see inventory efficiency worth playing with turnips. All you have to do is join an online group and someone will be having a jackpot day every day. You do have to share profits with the host but the scheme is still worth it.
This is a big economy mistake. 60,000 bells is quite a lot of money in AC, and a backpack full of turnips turns into 2,400,000 bells which is enough money to bypass most of the game. Avg item price is magnitude 3-4 so these are effectively free now. All from doing a single turnip scheme. Of course players will do this with multiple backpack loads and become deep millionaires living off bank account interest.
Nintendo's second mistake was to fix this exploit by attacking a symptom and not the root cause. They reduced interest rates by a magnitude, making it balanced for ppl with huge savings accounts and worthless for anyone playing the game as intended. We of course see the folly in this approach in OPs blog where his wife was punished for playing the game as intended. She is now incentivized to join the turnip schemers, making the problem worse.
Nintendo should either cap the amount of turnips you can sell on a friend's island, reduce the turnip value for island visitors, or disallow visitors selling turnips altogether. Then the bank accounts can remain as is.
Anyone with experience tuning f2p economies would have seen this leak a mile away and prevented it from ever happening. Now Nintendo only has bad options since removing player assets is never an option. Once you leaked you leaked.
Musings from a former f2p economy designer.