OMG, what an experience. We registered with Option town to fly return from Vietnam to Sydney. We were excited to receive a CONFIRMATION OF BUSINESS CLASS UPGRADE only to arrive at the check in and be met by an army of Vietnam Airlines staff who proceeded to laugh at our paperwork and promptly advise us that we were in economy. We were treated like "cheats" by Vietnam Airline staff, in particular one Senior Vietnam Airline staff member,Ms Tran T.[redacted], who informed us that Optiontown had no authority to upgrade us. We showed her our letter of confirmation from Optiontown and she laughed in our faces. We totally get that we may not receive an upgrade and we were fully prepared for that. But to have the confirmation given in writing and nothing at all appearing on the confirmation letter stating that it is still subject to availability and confirmation at check in, was just shattering. So, we came home economy and contacted Optiontown who apologised and said this was unusual. I pressed them and was finally directed to the "terms of service" at the bottom of the home page - told to scroll down and PRESTO...Hidden in section d. under UTo Service, there is was in all it's glory - " In the event of upgrade approved, upgrade decision remains subject to availability, passenger has to present a copy of the email to the airline staff upon check-in. If a passenger failed to contact airline staff for any reason the upgrade price for that flight will not be refunded. So, Optiontown's letter of confirmation means NOTHING.....it is still subject to availability and determined at check in. Trust me, when they look at you at Vietnam Airlines as someone checking in with an Optiontown upgrade confirmation, they treat you like something they want to wipe off their shoes. Then they laugh and happily sit you next to crying babies and rather large hairy gentlemen that sweat a lot......To add insult to injury...on check in they will try and say you will get business class service - just in economy seats........