When to Use Third Party Websites to Avoid Currency Conversion Fees?
 

I always prefer to book travel on a carrier's own website. You'll generally get more information, greater functionality, and more ability to clarify or modify, often free of charge.

From a cost standpoint, that breaks down for international bookings when you have to pay currency conversion fees (from the merchant, and/or the bank), credit card fees (with no other way to pay), etc. etc. that you might be able to avoid when booking through Orbitz, Expedia etc. from your home country.

How do folks determine when to go the third party route to avoid fees? And what transport services aren't available to book through them, such as low-cost airlines, rail and intercity bus services etc.?

I usually compare the difference between carrier (international sites) and booking sites.
I also have a CC that doesn't charge me for foreign transaction, so I just check the daily f/x rate and book via the cheapest source.

Edit: The only thing I learnt to avoid is a "three party booking". Last year I booked SAS flights, ticketed by LH, sold by Expedia. When I found that I had to leave early, I called each party three times and no one was able / willing to help me. Expedia told me that they can't rebook once I took the outbound flight, SAS told me it's an LH Ticket, so I should call them, LH told me it's an SAS flight sold by Expedia so I should call either of them. Major PITA, never again...

Which Card please? :)