Versprochen ist versprochen — a promise is a promise.
Zu seinem Wort stehen — to stand by one’s word.
Verbindlich zusagen — to accept in a binding way. Said of a person, unverbindlich means noncommittal, and it is not praise.
Bescheid sagen — to let someone know. Sag rechtzeitig Bescheid — let me know in good time.
Absagen — to cancel. An appointment is canceled, not simply missed.
Eine Vorwarnung geben — to give advance warning.
Hält, was es verspricht — it keeps what it promises, a standard phrase of praise for a product.