After a few days of betting, player called "zhent" managed to somehow win 200 BTC at betking.io What are your thoughts how is it possible some people manage to win so much? Just a matter of luck or is it the bankroll that is the key? It's very difficult to win with a very limited bankroll and it's coming from experience 
A post of the winner on BetKing thread: https://bitcointalk.org/index.php?topic=910134.msg13880555#msg13880555
A post of the winner on BetKing thread: https://bitcointalk.org/index.php?topic=910134.msg13880555#msg13880555
Yes, bankroll is an extremely important factor in the "quantity" one wins; however, percentage wise, bankroll size shouldn't matter. The key to being a successful player is bankroll management. Many serious players understand the Kelly Criterion and utilize that awareness to maximize their position. Sound bankroll management is a necessity if one wants to be a successful player.