What do you guys think about betting the river here and turning my set into a bluff, to bluff the opponent off of a straight? Surely they would think that the likelihood of me turning a two pair/set into a bluff is low and any straight draws got there and so wouldn't bet meaning from their perspective its very likely i have the flush.

PokerStars - $0.10 NL FAST (6 max) - Holdem - 6 players
Hand converted by PokerTracker 4

BTN: 76.7 BB (VPIP: 6.67, PFR: 6.67, 3Bet Preflop: 0.00, Hands: 15)
SB: 99.2 BB (VPIP: 11.11, PFR: 3.70, 3Bet Preflop: 0.00, Hands: 27)
Hero (BB): 402.7 BB
UTG: 141.9 BB (VPIP: 21.05, PFR: 17.89, 3Bet Preflop: 8.70, Hands: 100)
MP: 119.4 BB (VPIP: 19.23, PFR: 19.23, 3Bet Preflop: 31.25, Hands: 52)
CO: 169.3 BB (VPIP: 6.25, PFR: 6.25, 3Bet Preflop: 0.00, Hands: 18)

SB posts SB 0.5 BB, Hero posts BB 1 BB

Pre Flop: (pot: 1.5 BB) Hero has 9 9

UTG raises to 3 BB, fold, fold, fold, fold, Hero calls 2 BB

Flop: (6.5 BB, 2 players) 2 T 9
Hero checks, UTG bets 4.3 BB, Hero raises to 11.7 BB, UTG calls 7.4 BB

Turn: (29.9 BB, 2 players) Q
Hero bets 17.1 BB, UTG calls 17.1 BB

River: (64.1 BB, 2 players) J
Hero checks, UTG checks

Hero shows 9 9 (Three of a Kind, Nines)
(Pre 67%, Flop 94%, Turn 91%)
UTG shows 8 T (Straight, Queen High)
(Pre 33%, Flop 6%, Turn 9%)
UTG wins 61.2 BB

Definitely not. Considering you probably raise AK/AQss pre you can't have those, you can't have KJ/QJss, A2ss is about the only nut flush you can rep based on your action and i'm guessing you 3bet that pre some of the time, the only flushes you can reasonably rep are KQss and 78ss for the straight flush, do you bet KQss on the turn after you pick up SDV?

Basically on this runout you're repping super thin, you also have a limited number of K high straights (KJdd, maybe KQdd) and are you even betting those on the river? He also has way more flushes and K high straights in his range

This is a horrible runout for your actual hand, but you can check and win sometimes (vs QJs, JTs, or AA). On 4-liner 3-flushes like this, villain will usually play honestly. He'll check back very pretty often (even with straights), but usually has the nut flush if he bets, and you cooler him by check-jamming straight flushes. If you have any other flushes (or random Kx combos), you can check-call. With sets I think you just have to treat that river card as a "bad event" and hope it checks through.