Are the excess baggage fees shown on airline websites per flight or per ticket? Say I have a ticket with two legs (two flights) with the same airline company and X is the amount shown on the website. So, will they charge 2X since there are two flights involved?
Excess baggage fees are normally per flight but there are variations. In general, fees are charged at check-in time, so they end-up per check-in in most cases. If have to check-in separately for one leg of your flight, you will often be asked to pay the extra fee again. Arguing could help but in my experience they rarely budge, particularly if they are not the same airline as the previous leg.
In practice this means: Try to check you baggage and have it tagged all the way through. Even if you have flights back-to-back, as opposed to legs, you can ask the check-in agent to tag the baggage to your final destination while makes it possible to even skip an excess baggage fee.
Like any airline and flight, you'll have to check the terms and conditions on the ticket or the airline's website.
However, generally excess baggage fees are per flight, not per leg. So if you're flying from London to Sydney and the flight stops in Dubai or Bangkok, you'll only pay once for the excess bag. However, while that's the norm, it ALWAYS pays to read the terms for your individual ticket.