Originally Posted by
Phantasy
What I like to know is in short: do airlines know what a passenger booked at the travel agency (when it contains flights from another airline with no alliance between these two)?
If you mean do they know what a passenger
paid, then absolutely. It's right there in the e-ticket. Anyone having the e-ticket number and your details can see everything about your ticket. And all airlines involved have all that information.
Look up your reservation on any third-party PNR viewer (Saudia Airlines is a good one for Amadeus PNRs). The fare information and amount paid, usually with the tax breakdown, is all there in the e-ticket.
Here's an example of a KL ticket booked on a third party OTA, viewed on the Saudia website: