Is this standard against unknowns? Should I bet the river with mid pair because the board paired? What if it didn't pair?

Cryptologic 1.00/2.00 Hold'em <font color="#0000FF">(6 handed)</font> link

Preflop: Hero is BB with 3[img]/images/graemlins/heart.gif[/img], 7[img]/images/graemlins/heart.gif[/img].
UTG calls, <font color="#666666">3 folds</font>, SB completes, Hero checks.

Flop: (3.00 SB) 7[img]/images/graemlins/spade.gif[/img], Q[img]/images/graemlins/club.gif[/img], 6[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, UTG calls, SB calls.

Turn: (3.00 BB) 8[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, UTG calls, SB calls.

River: (6.00 BB) 8[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, Hero checks...