Originally Posted by
CPH-Flyer
Price, validity period, and number of seats available for the fare as the main differences
I would add fare conditions as well - such as cost to amend sectors, cost to cancel and so on.
These conditions for deeply discounted fares do need to be checked carefully - I had a THAI J fare once that had stricter conditions than a usual J fare: specifically, no sector could be amended until AFTER the first sector was flown. I cancelled and re-booked with the changed dates as this was cheaper....