Tax free in Armenia has some peculiarities: if a traveler buys something in Yerevan and it’s price is more than 100.000 AMD, than the tax free service can be activated. You just need to ask the cashier whether their shop has a tax free service (you can check on the shop windows also before entering). If yes, than the cashier should give you a specific card, which, when leaving Armenia should be shown on the border or in the airport.