$1800 first class ticket Boston to Las Vegas. A problem with the plane forces them to cancel the flight; annoying, but stuff happens.
At the gate they tell me they can put me on a later flight, but no first class seats, and they give me a number to call to get the fare difference refunded (coach fare is approximately $400).
3 months later, they have refused to refund the fare difference. After many different stories, they've eventually decided my first class ticket (purchased as such from their own web site) was really an "upgradeable coach" ticket.
Completely untrue, absolutely nothing on their web site or ticket (which had an assigned seat). Wish me luck in small claims court!
Review about: Delta Airlines Flight Booking.