As above posters said, playing online blackjack isn't smart. If you're an expert blackjack player the house edge is around 0.5%. Either way, it's very possible these online casinos are indeed rigged to an extent. It would be almost impossible for them to get caught if they programmed another 1-4% advantage for them, or gave them a higher probablity of winning when you up your ante. Even if they did get "caught" somehow, do most online casinos even claim to offer real casino odds?
If you're going to play casino games, at least go to a casino.