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 major poker sites have detection protocols to prevent bot play, but some of the more sophisticated bots are able operate undetected, and some poker sites simply don't care about bots since their play produces rake (though, they will ban a bot if they catch it, or if it's reported).