BOS-JFK: Delta
JFK-IST: Delta
IST-CDG: AF
CDG-BOS: DL codeshare with AF
I have seen the same flights on the DL website, but the cost is much higher than the prices on Expedia, Orbitz, and Vayama (all of which range within a few dollars of each other and are ca. $800 less expensive than Delta).
How does it happen that at least three third-party sites are showing the lower price, but a DL agent can't see the lower fare?