Online gambling sites are businesses (including stake). Their goal is to make a profit. They can easily rigged a bet to make sure that they'll get the profit they want without being suspicious. They can easily do it, like for example.
User - 1, 3, 7 , 9 , 11 , 13 will lose (3.2BTC) on monday // User 2 , 4 , 6, 8, 10 will win up to (2.2BTC) on monday = the sites takes the 1BTC as there profit. They can set there system to shuffle the users or generate the losing users and winning users. lol wth dugo na ilong ko. You guys know what i mean!