So, think you're making lots of bells catching beetles, huh? Cool, cool. But what if I told you that you coulda sold that last gold stag for over 50,000 bells? Or that horned atlas for over 30,000? And what if I told you that you could sell it at that price all night long, after all the stores have closed?
Get yourself a campsite if you don't have one. All campers offer to sell furniture or buy items, but only the lazy type is GUARANTEED to buy for over 4x the normal price. When a camper with the "lazy" personality type shows up, it's time to rake in the bells.
Load up on palm-tree beetles, sharks, and whatever other super-expensive fish or bugs you can find. Leave behind any tools you have unless they're gold or silver, and leave behind clothes/accessories/anything else. Campers will only play games if you have 1 free inventory space and at least 5,000 bells, so check to make sure you're okay on inventory and bells before you head to the campsite.
Talk to the lazy camper over and over again, until he offers to buy one of your expensive bugs/fish with a game called "What Do I Want to Eat?"
He'll start with a clue regarding the color of fruit he wants to eat. Depending on the clue, you'll get 4 choices.
"The color of the fruit I want to eat is not red."
Apple (it's never this, obviously)
Banana (don't pick this yet)
Orange (pick this)
Pear (or this)
If you're lucky, you'll win right away, and he'll buy your bug/fish for an insanely high price. If you're not lucky, don't worry. Next clue.
"If I described the shape of the fruit, I would say it's long/round."
Apple (never pick this)
Banana (long)
Orange (round)
Pear (round)
Since you picked pear or orange in the first round, there should only be one correct answer left.
Alternatively:
"The color of the fruit I want to eat is reddish."
Cherry (pick this)
Peach (don't pick this yet)
Strawberry (or pick this)
Grape (never pick this)
"If I described the shape of the fruit, I would say it's bite-sized/round.
Cherry (bite-sized)
Peach (round)
Strawberry (bite-sized)
Grape (never pick this)
Since you picked cherry or strawberry in the first round, again, there's only one correct answer left.
And you win. EVERY TIME. There's no way to fail on this. They pay at least 4x what it's normally worth. That means, with just a little extra work, you can quadruple your island farming profit. Less trips to the island, more money for your bank.
All campers can potentially buy your items for 4x the value, but only "lazy" types have a 100% success rate.