Why didn't your friend complain at the time?
Personally I would have asked for a refund had it been that bad and if the staff within in the lounge were not forthcoming I would have asked to speak to the airport duty manager and made a complaint through that channel. They incidently would have been able to supply your friend with the business in questions particulars in order to make an official complaint to their head office.
Furthermore, if it were as bad as you are suggesting on behalf of your friend I would have about turned and walked out (after demanding refund) before I even got to the stage of checking whether it was Smirnoff or Tesco Value Vodka