How would you double $100 in a month?
Imagine you have $100 and you need to double it in a month. What would you do? How would you replicate it again with $200,$400,800,$1600 and etc.?
I'm joking. But the question is kinda crazy because it doesn't scale. You're asking for a 100% return in a month. That's 4000% or more annualized return... Assuming you're starting with that initial capital and you want to keep it working. For those returns you need to take massive risks.
Gambling is one way. Options markets is another. (See gambling)
Lightly-used items can be sold on eBay, while vintage items can be sold on Etsy.
After that, cars and pickups trucks can also be arbitraged by going to car auctions and watching Craigslist. It especially helps if you know a mechanic well or are a mechanic.
The next step is arbitraging small businesses and real estate.
Beyond that, you need to slowly build a real portfolio of defensible business investments.
I remember some research that found low level drug dealers didn't make much more than a typical low wage job... sometimes way less. Many had low wage jobs because of that.
Find investors who would give you 10$ commissiom on hand registered finds, so these investors pay 20$ per name instead of 10$.
You never have to shell out a penny pf your own.
For some domain investors, saving the search is worth the 10$ extra cost.
Back up your quality finds with data.
Rinse and repeat.