Should I raise on the river here?

stakes - $.5/$1

button - $86
villian sb - $203
hero bb - $99

The villian is a passive player that does not always bet top pair, and I haven't seen him bluff or semi-bluff.

Dealt to hero: 4 [img]/images/graemlins/spade.gif[/img]8 [img]/images/graemlins/heart.gif[/img]
sb $.5 and bb $1 posted

button - calls $1
villian (sb) - completes $.5
hero (bb) - checks

Flop ($2.85)- 7 [img]/images/graemlins/heart.gif[/img]5 [img]/images/graemlins/diamond.gif[/img]6 [img]/images/graemlins/diamond.gif[/img]

villian - checks
hero - bets $2
button - folds
villian - raises to $4
hero - calls

I didn't put the villian on the flush draw because he is not that aggressive, he definately has a hand. I think he could have had top pair, overpair, two pair, set, or a straight. The only flush draw would be something like A [img]/images/graemlins/diamond.gif[/img]7 [img]/images/graemlins/diamond.gif[/img]. Since I didn't think the flush was a threat I didn't raise because I want him to bet out the turn and I don't want to reveal the strength of my hand yet.

Turn A [img]/images/graemlins/diamond.gif[/img]

Villain - $5.4
Hero - Calls

He couldn't have had A [img]/images/graemlins/diamond.gif[/img]7 [img]/images/graemlins/diamond.gif[/img] because the ace hit. But he could have had 7 [img]/images/graemlins/diamond.gif[/img] and something else of [img]/images/graemlins/diamond.gif[/img]. I didn't think it was likely. Maybe he hit is ace here for two pair. I didn't raise here because I wanted him to bet out the river but maybe that isn't such a good idea because the 4 flush could hit.

River ($10.45)- K [img]/images/graemlins/spade.gif[/img]

Villian - bets $7.1
Hero - raises to $20

With the ace and the king falling and him betting the river means he definately has more than one pair. And this is the point of the post because he is a very passive player. In hindsight for a passive player to even bet out ~2/3 the pot on the river with such a dangerous board he must really have a hand. I could have the flush here for all he knows. Only the flush and the nut straight beat me here. One pair has been ruled out. So the problem is would he bet out and then call a raise with two pair, a set, or the low straight (if he would complete the small blind with 34). The question to ask is: if he calls can I win at least %50 of the time. I didn't have a lot of time to consider it and I didn't want to be weak so I raised on the river.

Any advice or comments?