Tough river spot vs. unknown

[Pokerpudel]

Played the first time with this guy pretty much no history. Have him 28/9/0.85 on~500 hands I think it would be an easy call if he would bet half the pot but shoulod I call a potsize bet there?
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Played at Prima Poker
5 players, seat 6 is the button

Seat 1: SB ($746.50)
Seat 2: <font color="#C80000">Hero</font> ($620.70)
Seat 3: UTG ($317.10)
Seat 4: CO ($29.40)
Seat 6: BTN ($111.93)

SB posts small blind, $1.50
<font color="#C80000">Hero</font> posts big blind, $3.00

Dealing to <font color="#C80000">Hero</font>:
K[img]/images/graemlins/club.gif[/img],Q[img]/images/graemlins/spade.gif[/img]

UTG folds
CO folds
BTN raises to $6
SB calls
<font color="#C80000">Hero</font> raises to $21
BTN folds
SB calls

Dealing flop: (Pot is $48.00)
J[img]/images/graemlins/diamond.gif[/img],4[img]/images/graemlins/heart.gif[/img],3[img]/images/graemlins/club.gif[/img]

SB checks
<font color="#C80000">Hero</font> bets $31
SB calls

Dealing turn: (Pot is $110.00)
8[img]/images/graemlins/heart.gif[/img]

SB checks
<font color="#C80000">Hero</font> checks

Dealing river: (Pot is $110.00)
K[img]/images/graemlins/heart.gif[/img]

SB bets $110

[Merlinius]

probably fold. the flop was very dry so he can't have a missed draw. very often big bets like this on the river are desperate attempts to get value after the turn c/r didn't work out - especially because the K hit and you could very well have AK. If he had a J, this big river bet would not make any sense because he would want to get a cheap showdown with it.