There is a live video platform in China called Douyu who offers virtual currency gambling, from which I find out a very interesting phenomenon - the return rates always stay low, i.e. on specific conditions when the outcome is a random event (50% chance on each side), the return rates always stay below 1 (often 0.1 - 0.7) on both sides, rendering it unfair for any gamblers who pays - take it or not.