Online poker sites that are legitimate and have passed through third-party scrutiny are NOT rigged. But some players won't believe this, and feel they are being cheated over issues such as: Too many bad beats. More pots being won by depositing players (to encourage new players)
Most people only talk about it being rigged after a big losing session or a bad beat in a tournament. The fact that so many online poker players have made hundreds of thousands, or even millions of dollars playing the game, proves that the games are not rigged.