So here I have a friend who's inviting me here on the said gambling investment. It's just simple, you'll send your bitcoin (investment on any amount) on that person then he's going to play using the money collected. After 7 days, your investment will be doubled and the money will be sent back to you after deducting the trans fee. There is a chance of losing but if your money loses, you'll. Be given a 10% refund.
Someone already tried this? Safe or not??
I think you are talking about ponzis here. Ponzis are usually run by a person who collects the money and tries to invest in some places, if he gets a good return, he will share the profit with the investors and if he doesn't, he will simply run away. Unless you know that person personally, don't expect to receive even 10% refund. This is the riskiest investment for any market, be it crypto or fiat. So if anyone is trying to pull funds in the name of gambling investment, you should report that in "Scam Accusations" sub-forum so that a proper action can be taken against such people. Please note, that bitcointalk doesn't support such kind of activities here.