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good preflop against unknown. I pretty much bet this flop every time...

Since you checked flop just give up on turn...

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I agree. It's easier for you to take his blind by betting the flop. Raising preflop will usually get a call. Not too many players will limp/fold from the SB.

Also, the bigger you make the pot preflop, the more likely it is that he will find a way to showdown with you. I'm sure you don't want that with 5 high. Bet the flop when he checks and give up to any resistance.