76o

Bet out with your pair is fine and bet Turn is Standard as well. You gotta find out whether your opponent is capable of betting himself when he got nothing and how lose he calls on the flop and based on this information sometimes play check/call with weak hands but midpair on this board is just too strong and this guy is lose and will certainly call against the odds with overcards and lots of backdraw possibilities.

But most of the times it's better to bet out yourself and not hope for inducing a bluff against such a passive guy who's likely to chase a lot but taking the freecard if possible. 78 got there on the turn but that's just the only hand you have to worry about and this guy probably doesn't even raise with a weak 9 but bet if you check and you can charge him for all his gutshots.

On the River i would check as well because he won't call that many worse hands but a lot of his hands are still busted. Like any 7x 8x Gutshot type of hand. T7 T8 etc and he could check back with a better 6x. Better hands he won't ever fold and since this card is so scary sometimes you might even see a free showdown against 9x. A valuebet is just too thin. I would recommend check/call River and hope to catch up a busted draw.