Forgive me if wrongly posted. I fo.und a great flight on ITA. The first small segment is AS and the remainder is Singapore. The international destination is not bookable on AS and the small first segment airport code isn't found on Singapore. Even if I eliminate the first segment, I can't come close to the fare on ITA or with Expedia.
PSC-SEA-SIN-CMB. I can see all the fare breakdown for use with a travel agent.

My questions are, how often is ITA really off in its pricing and can anyone recommend a site or travel agency willing to listen to all the fare information and try to find what I am looking for?

I apologize for my ignorance and would appreciate not being trashed.