Obnoxious flop check ?

[Tropex]

Party Poker 0.50/1 Hold'em (6 max, 5 handed) pokerhand.org hand converter

Preflop: Hero is Button with J[img]/images/graemlins/spade.gif[/img], A[img]/images/graemlins/spade.gif[/img].
<font color="#666666">1 fold</font>, MP calls, <font color="#CC3333">Hero raises</font>, SB calls, <font color="#666666">1 fold</font>, MP calls.

Flop: (7 SB) J[img]/images/graemlins/club.gif[/img], 3[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, MP checks, Hero checks.

Turn: (3.50 BB) 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">SB bets</font>, MP calls, <font color="#CC3333">Hero raises</font>, SB calls, MP folds.

River: (8.50 BB) K[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, SB folds.

Final Pot: 9.50 BB

How's my line ? I figured they won't fold anyway (SB was 40/something small/something small) is it okay to wait for turn ? Also these guys have the tendency of betting turn what ever falls when the flop is checked so it actually gains value, no ? Is it too risky, since I'm 80% (or something) sure they won't fold