LATB 7 handed. Effective stacks don't come into play, but effective roughly 20k.

Art raises sb $350, garrett calls bb, nick calls straddle.
Flop ($1050) Kh7h6d
Check x3
Turn ($1050) Kh7h6dTh
Art check, Gman check, Nick QhJs bets $400, Art calls $400, Gman check raise to $2,000

(makes no sense at all to check twice and squeeze here imo. What would you range Gman with?)

Nick calls $1600 more, Art Td9d folds.
River ($5450) Kh7h6dTh3s
Gman bets $5,000. Nick folds his QhJs for sdfd that missed.

Gman has Ks9h. Is he bluffing or value betting?