Have to agree with most people above, I would bet the pot, you're not giving them the odds for the flush draw so you will win in the long run.
I make the odds of them having a higher flush as 8/47 * 4/46 = 1.5% as there only 4 higher spades than your 9.
If they have higher flush so be it, but chances are that small that in a STT you have to ignore that small chance, imo.
