Thank you for your post, LeMahDi. I used to be VERY cautious of such flops too. I may have been too paranoid. But, what can villain possibly have here that make a flush? KQ, QT, T9, perhaps even 98 of spades... maximum of 4 combinations unless he has a wide 3-betting range. I'd play it in any of the following ways:
1. fold preflop (It would be too expensive to 4-bet and A9s is not that good.)
2. call on the flop and fold to a bet on the turn unless the bet is too small suggesting weakness (for pot control)
3. call on the flop and bet or raise on the turn and fold to a re-raise in the attempt to get a showdown for free (a little expensive)
I'd be more scared of AK (8 combinations), AQ (8 combinations), AJ (6 combinations), and AT (8 combinations) than a flush (4 combinations). But, there are cards that you have beat too. KK (6 combinations), QQ (6 combinations), TT (6 combinations), 99 (6 combinations), 88 (6 combinations), KQs that are not spades (3 combinations), and many others if he has a wide 3-betting range. In fact, against the range with the top 10% hands, you still have around 49.30%