The platform I currently use does only 10%.
I offer the Pay NaMaidani payment system, where you can receive interest on deposits in several cryptocurrencies. Go to the investment section and choose the plan you need. Here is the condition for BTC investment:
Invest 0.1 BTC for 3 months with a fixed income of 0.0036 BTC. You will receive daily interest payments of 0.00004 BTC to your wallet. Full return of investment at the end of the term.
What sort of *send me 100 dollars and I'll send back 500 dollars* kind of scam is this?
Sorry, but there is no scam in the investment plan offered in my post. Users already use exchanges or keep cryptocurrency in their wallets, keeping it in the payment system allows you to get 14% per annum, which is mutually beneficial for the user and the company. In your post, it is not clear what is 100 and what is 500, because I have an amount of 0.1 indicated, to which a person will receive an interest of 0.0036 for three months and a total of 0.1036 until the return. Therefore, your example is unclear, or you are careless, or you selected the example in the wrong entry.