3/6 77 river valuebet?

[bottomset]

villian is unknown, just sat down a couple hands ago.

Party Poker 3/6 Hold'em (6 max, 6 handed) converter

Preflop: bottomset is MP with 7[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/heart.gif[/img].
<font color="#666666">1 fold</font>, <font color="#CC3333">bottomset raises</font>, CO calls, <font color="#666666">1 fold</font>, SB calls, <font color="#666666">1 fold</font>.

Flop: (7 SB) 5[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/spade.gif[/img], 6[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">bottomset bets</font>, CO calls, SB calls.

Turn: (5 BB) J[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">bottomset bets</font>, CO folds, SB calls.

River: (7 BB) J[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, bottomset ?

is this an easy river bet against an unknown?
how about if the river was the J [img]/images/graemlins/diamond.gif[/img] or J [img]/images/graemlins/club.gif[/img]?