I am also jealous of people that won hundreds of BTC on gambling sites.. so I always try to bet and see if I get lucky enough.. never happened.
the top winners is not always real, or maybe they actually are men of the houses. it happened on manga Kaiji, there is a gamble game, only 2 winners for 10 years, and those 2 winners actually are 2 top bosses of the casino. not sure if it happened in real world or not, but i believe there must be.
Yes we need to try to join those sites which do not scam us. Some sites will show you the real status but there are a number of sites which show fake usernames of the usernames of that who are the owners of the sites. Whenever you join a site try to search its reviews on google. In short if you join legit sites, then you will also earn.