The tight reg who calls your 3-bet out of position and then check-calls the flop and turn is on a draw or he has a hand he's not confident about. When the river bricks and he checks, he's done. Bet it.

Why they do it

Tight regs at $1/$2 who call 3-bets out of position and then check-call two streets are almost never trapping. They have a hand they wanted to continue with but they're not confident enough to lead. When the river changes nothing and they check, they've given up. They just need one more reason to fold.

The adjustment

Bet the river with a reasonable size. You don't need to overbet. A 60-70% pot bet gets the fold from a tight reg who check-called two streets and missed.

What it's worth

Checking back a river against a tight reg who was clearly on a draw because the board looks dangerous leaves $50-80 on the table. They're folding. Make them do it.