Когда моя подруга хотела купить билет в кассе, ей сказали что, все билеты уже проданы.
When my friend wanted to buy a ticket in the bookoffice, she was told, that all tickets had already sold
had already been sold - пассив, ведь билеты проданы.
When my friend wanted to buy a ticket in the box office, she was told that all tickets had already been sold.
booking office
Смотря какие билеты. Если в театр, то
When my friend wanted to buy a ticket at the box office she was told that the house was sold out (можно и без перфекта, по состоянию на тот момент) .
http://www.thefreedictionary.com/sold-out
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