As someone whose only experience "trading" is buying some alts in an exchange, I know it would be hard to have a consistent profit. Sure someone trading stocks may be able to spread the risk by taking money from multiple investors and diversify but it's no assurance that nothing will go wrong and all the money will not go up in flames.
If have money I can invest I'd rather just buy and hold BTC or loan it out to people I know.
TLDR: don't trust anyone offering you a fixed rate of return, if it sounds too good to be true then it probably is. Great advice but very much over-complicated here.
A fixed return is possible if the creditor is absorving the risk.
Creditor runs risky investments using your money, but gives you fixed returns in exchange for lower yield. This is fine as long as there's oversight over liquidity to guarantee the fund manager didn't lose it all - it'd then become a ponzi.
Your correct but a lot of these scammers offer unrealistic rates that will never be reached. If anyone had such a sound strategy they could come up with at least a small amount of money themselves and grow it exponentially without needing outside funding sources.
But of course they'll just say that they may have come up with a good idea but they are too broke and have no access to credit to accomplish it themselves.