I got that badge in a weekend, completely legit. No help from TBT or anything. But, my method requires the following:
1) a separate DS
2) a separate game cartridge/digital copy of ACNL
3) time and patience
4) The ability to largely Time travel for possibly weeks/months at a time
5) At least a million bells to start out with
If you have all of those things, here's what you do:
Step one: Grab your main DS (we'll call it DS-A) and game and set it for 6 am on the nearest Sunday morning.
Step two: Get on the other DS (we'll call it DS-B) and put in the cartridge of the town you DON'T want to make money in right now. Power it up and set it for 9 am on the nearest Monday morning.
Step three: On DS-B, check the turnip price. On DS-A, buy as many turnips as you can hold (you should also clear out your train-station locker so you have all 180 spots, plus your inventory space).
Step four: This is the most tedious step. If the price isn't acceptable on DS-B, time travel to Monday at 12pm (when Reese re-sets the price) and check again. DO NOT, UNDER ANY CIRCUMSTANCES, TIME TRAVEL ON DS-A. IF YOU DO, THE TURNIPS WILL SPOIL AND YOU WILL LOSE WHATEVER MONEY YOU SPENT. If the price still isn't acceptable, repeat with the next day (Tuesday at 9am, then at 12pm). Keep going until Reese is selling at a price that's fantastic, even if it's weeks in the future (I kept going until she offered turnips at a price of 520 bells!)
Step five:Found a price you love? (don't settle for prices you like! I promise, Reese will eventually sell for up to 600 bells if you have the patience to TT!) Now it's time to sell, sell, sell! On DS-B, open your gates to visitors, and AFK.
Step six: On DS-A, go to the train station and visit the town of DS-B (don't worry, it won't count as time-traveling, so going to DS-B, despite the huge time gap, will NOT affect your turnips). Once you're there, go to Reese and sell everything you have!
Step seven: Repeat the process until you have enough money!
~Side notes~
*You may have to TT backwards if Joan is about to leave (she leaves at 12pm!)
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DO NOT TIME TRAVEL BACKWARDS IF YOU STILL HAVE TURNIPS! MAKE SURE YOU SELL THEM TO REESE BEFORE TIME TRAVELING OR THEY WILL SPOIL.
*When I was doing this, I made about 9 million each go around. You would have to do it about 4 times to get the rest of the money you need.
*Without breaks or distractions, it took about 15 minutes to buy the turnips and sell them each time.
*If you don't have an extra DS, there are people on here that are willing to let you swing by and sell turnips to Reese. Be advised, however, that they probably won't let you keep coming back as much as you would need to.
*
This is the guide I used for stalk market guides.
!!If this method doesn't work for you, and you'd prefer to get your money without the help of TBT for IGB, here are other ways to make quick cash!!
*Fruit! When I built my first town, I made a tree farm of all of the fruit (except for local) and sold it. I had so many trees that I made about 300,000 every three days!
*Fish and bugs! This one's a no-brainer. You can make a good 300,000-500,000 by fishing/catching bugs for a few hours!
*Selling unwanted unorderables/villagers to members of TBT, and requesting you'd prefer IGB than TBT.
!!Hopefully this helps! If it doesn't, maybe it'll help someone else down the road!!
