There are exchanges that give you interest for holding the coins but i will not trust them either.
Exchanges that are running for long can be trusted that they would not steal your money - the problem is with the hacks and big reputed exchanges are often the hackers targets. The legal battle after that can be tiresome and frustrating and it is wise to avoid this altogether.
But the third party sites specializing on acting like a bank to give loans and take deposits, I would rather keep my coins in a wallet whose private keys are under my control.
When it comes to random messages posting returns, hell no way, block and move on

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That is a no-brainer, mate. People who fall for those need to stop investing in cryptocurrencies.
I earned a huge amount of interest few weeks ago when the price of bitcoin increase to $67 before the price started decrease to $60 few days ago in the market. It was not a small risk I took to observe the market price very well for me to be able to achieve my interest from the investment.
The topic is for interest earned on staking bitcoin on sites that offer to do so. What you earned, congrats for that, is from speculative market trading. These two are different.