The tight reg who flats your turn bet after calling the flop is not giving up on the river. He has a hand that's good enough to see it through. Don't bluff the river into him.

Why they do it

Tight regs at $1/$2 don't call two streets with nothing. By the time he's called flop and turn he's committed to seeing the river and he has a reason to be. He's not folding unless the board completely destroys his hand.

The adjustment

Check back the river with bluffs. Value bet the river with strong hands. Don't try to push him off a hand he's already decided to call with - it won't work.

What it's worth

River bluffs into tight regs who called two streets are one of the most reliable ways to spew chips at $1/$2. Check it back. Save the bullet.