。
All reservations are advance sales.
Literal
Reservations [topic-は] all advance-sales be-[formal-である].
A terse formal-written claim, as you'd see on a ticket sales page. 前売り ('advance sale, pre-sale') is a noun built from 前 (before) + 売り (selling), a common business term. The formal copula ~である places this in written register; in speech you'd use ~です.