Playing 7th street is very dependant on situation:
a) How many opponents are present ? For example, if you have three Kings with two of them showing OOP of position and check and someone with two Queens showing calls someone with two Aces showing, calling is the only right play as you can beat both players but are never getting a call if you raise from a worse hand.
b) If HU, it depends on your opponents. If you think an opponent is more likely to bet a hand that you beat than he will call with one, checking for value (and sometimes c/r) is best. If it's the opposite, betting is the way to go.
c) Depends also on your % of having the best hand at showdown. If you're sure you have the best hand (you have trips showing but in reality you have a FH) against something that looks like a str8, betting is probably best, you should go for a c/r since nobody will raise your bet and you stand to gain two bets more often than if you bet (wich is just one bet and you sometimes get a fold). On the opposite, if you're 60% sure of being beat, c/c if pot
odds dictate SD is the way to go.
My guess is the second scenario in c) happens a lot to you and your hand reading/thinking skills could need some twinking: if you don't know where you stand, c/c is the best option since it minimizes mistakes. Thus, playing passively is a sign of wanting to go to SD by sacrificing possible bets. The tradeoff is less money in the long run.
Scenario: let's say you have a small pair showing, but in reality, you have a small str8. Someone with a coordinated board (JsTs2s3x) is in position against you and he has raised you on 5th but not on 6th opting to only call your bet. If your opponent had a four flush and you have two spades in your hand (that are not showing), he will be more likely to NOT have a flush even though he raised you on 5th. He can have a bigger straight, two pairs or a set. Thus, if you bet and get raised, this can be a very large number of hands and you should be semi-glad you have bet since you gain more the good number of times your hand is good (high two pairs could raise for value here against your lower pair showing).
Had you not had the spades in your hand, c/c might be best since the chances of your opponent having the flush + bigger str8 are greater. So really, c/c is not bad per se, but it shouldn't always be your default line or you'll be passing on value, especially in a game like 7hi Stud where you don't see too many showdowns and you gain a lot by making second best hand pay.
