Good spot to double barrel?

[Bubsy27]

Full Tilt Poker
No Limit Holdem Ring game
Blinds: $0.50/$1
5 players
Converter


Don't know anything about villain,but lets presume he's reasonably tight and a pretty average/half decent player.

Pre-flop: (5 players) Hero is Button with 6[img]/images/graemlins/spade.gif[/img] A[img]/images/graemlins/heart.gif[/img]
2 folds, <font color="#cc0000">Hero raises to $4</font>, SB calls, BB folds.

Flop: K[img]/images/graemlins/club.gif[/img] 9[img]/images/graemlins/club.gif[/img] Q[img]/images/graemlins/heart.gif[/img] ($9, 2 players)
SB checks, <font color="#cc0000">Hero bets $6</font>, SB calls.

Turn: 8[img]/images/graemlins/diamond.gif[/img] ($21, 2 players)
SB checks, Hero checks.

River: 2[img]/images/graemlins/spade.gif[/img] ($21, 2 players)
SB checks, Hero checks.

Results:
Final pot: $21

When villain has checked the turn can we presume he doesn't have a king and go ahead and bet. On the river its obvious he's scared, but if we bet now it doesn't it look like we are weak and will he call with a 9? a Queen or a lower pocket?