If you play a lot of poker online in the low and "micro" limits, there's a scenario that comes up surprisingly frequently in no-limit hold'em games in hands that reach the river.
On fifth street, a player makes a very strong hand. For example, having called from the blinds with , the player continues to check-call as the board runs out . That river spade nicely completed the nut flush for the draw-chasing player, setting him up to win the pot.
What happens after the river is dealt? The player checks again, motivated by an idea to check-raise after his opponent fires another bet on fifth street.
But his opponent doesn't bet, and instead checks behind. The player shows the nuts and wins, perhaps eliciting a "wow" in the chatbox — or maybe a sarcastic "gh" — but no extra chips.
It's amazing how often players show up with monsters on the river in these games, even the stone-cold nuts, yet somehow fail to bet their hands after having made them at some point postflop.
These aren't marginal, "thin" value bet-type situations where there exists genuine doubt about a player's relative hand strength. For example, a player with pocket nines calls a raise from the blinds, sees an overcard flop and check-calls a bet, then after the turn goes check-check decides to check the river rather than bet with what might be the best hand.
No, this is having either an unbeatable hand or an especially strong holding that is almost certainly best, but failing to flip the switch from "passive" to "aggressive" mode and actually bet the hand.
A safe rule of thumb at the micro stakes online and even in some low-stakes live games is to avoid the "fancy" play and be more straightforward in these spots. That's because in order for such plays to work, they usually require a higher level of thinking from your opponents than is generally on display. Nathan Williams outlined this point in an article here a while back titled "The #1 Mistake in Small Stakes Cash Games: Fancy Play Syndrome."
The only reason to try a river check-raise for value in situations like this is if you are certain that checking your big hand is the only way to get an opponent to commit more chips to a pot you stand to win. That means being sure your opponent (1) will fold if you bet, and (2) will bet if you check.
Your opponent may not be paying attention to you, but you have to have been paying attention to him in order to know these two things. You have to have watched him well enough to know, for example, that he's capable of folding if you were to bet. Or that he's loose and aggressive and likely to fire again on the river if you check. Or that he's given to bluffing and so is likely to bet even with a weak hand if you check.
There are occasional instances when check-raising the river can be an effective play even in these low-limit online games, including as a bluff when you are near-certain an opponent is betting with medium or weak holding. But that, too, is a relatively "fancy" play that isn't necessarily worth trying that often against such opponents.
In games with attentive players, checking a monster on the river and then watching an opponent check behind isn't necessarily all bad. You lose potential value, sure, but you also create doubt in opponents' minds about whether or not you might be trying to trap them when checking subsequent rivers. They'll stop making those "thin" value bets against you, remembering how you checked to them with the nuts before.
But in low and micro stakes games, your image isn't as big of a concern. The player who checks behind is less likely to place any great significance on your having checked a big hand other than to be thankful he avoided losing more in the hand. In fact, it's more likely your opponent will be congratulating himself on losing less than giving you any extra credit for "clever" play.
You made your hand — bet it!