I didn't take notes on this hand, so I don't have all the specific numbers, but they aren't that relevant to the end question.
$40+10 live bounty tournament

So with a limp in front (young, timid player, we're in the first level though so no solid read), hero opens A8cc preflop in mp (standard raise is 3x+x for each limper, so probably that). One call immediately to my left, and limper calls immediately to my right, so we're three to the flop with probably 675 in at 25/50 blinds.

Flop comes 5s6c9s, limper checks and hero bets 300. V2 folds, limper calls.

Turn (pot ~1275), 4c. V1 checks, hero bets ~800 (with intention to check back bricks on river), V1 calls.

River (pot ~2875), Qc. V1 checks. This is the textbook spot for a polarized bet, right? Front door flush misses, so if villain had a flush draw he isn't calling much, and polarizing our bet will entice sets and straights to bluff catch, right? Effective stacks at river are about 6k, villain effective.

If you were V in this hand, would you flat call flop and turn with a set/straight? Obviously no.
So the question is from what hands you can get value. Most probably one pair hands

You got 2 streets post and you got him to call the iso-raise pre.
With this info, it's easier to value bet no? Don't go too big
Between 1/3 and 1/2 it is ok

Advice, open some range software and assign a range for villain and try to narrow it down with each street. You will see that he doesn't have strong hands the way the action was played

Interesting. I see what you mean from a theoretical perspective (obviously I would never play a set like that), but I think the read of "scared money" of the villain helped me a lot here.