The game of blackjack is one of the most balanced casino games, be it online blackjack or blackjack found in a brick and mortar casino.
Think about it for a moment. The odds of winning blackjack are 48% and the odds of losing are 52%. That is actually pretty even in terms of odds of winning. The reason for the fairly even odds of winning or losing comes from the fact that blackjack is a pretty balanced game.
The balance is from the structure of the game, from its rules. See, look:
For every house rule that gives the player some sort of advantage in terms of odds, there is some aspect of the game that will counter balance it. Take for example the house rule that has the dealer standing on all 17s, that is one rule that benefits players because once the dealer reaches that 17 there is nothing else he can do, and if he has a hard 16 he still has to hit it even though it is likely that he will bust.
To counter the increase in player odds, the house will also be using multiple decks at that table. It is not a normal occurrence to find a game of single deck blackjack and that also has the dealer standing on al 17s.
Another example is a blackjack game played with two decks that does allow the dealer to hit a soft 17. But in that game players are allowed to double down on any of their first two cards, not just 9s, 10s or 11s, double down after splitting pairs and resplit pairs up to a set number of hands.
If you study the house rules and the number of decks being used, you can get a pretty good idea of whether the blackjack table you are looking at is balanced enough or not. And if you observe that the rules and set up lean heavily on the house, you know not to play at that blackjack table, and to keep looking for a balanced blackjack game.