Investment in casino bankroll is also highly predictable. I've spend few years on stocks. Seeing insider trading, fake quarter financial reports (corrupt officials let them pass), instant 0 in 1 day when this scam come out. Nothing is 100% zero risk investment.
I estimate exist scam (major risk) at ~10% (casino earns 50% of bankroll in 1 year), 20% if bitcoin will pump to 20k+ (high bitcoin price gives better financial motivation for exit scam, in some cases you are doomed to exit-scam because of high bitcoin price (implementing fractional reserve system before)). So if my investment yields 50% annually than it is good risk/reward ratio.