我向你保证。

I promise you.

我向你保证我会保守秘密。

I promise you I'll keep it secret.

你可相信我。

You can trust me.

我会信守承诺的。

I'll keep my promise.

我说话算数。

I mean what I say.

他是个说话算数的人。

He is a man of his words.

我不会让你失望的。

I won't let you down.

我发誓。

I swear.

我不能保证。

I can't promise.

我不能向你许诺什么。

I can't promise you anything.

他们包退包换。

They guarantee the exchange or refund of the goods.

我会尽我所能帮助你的。

I'll do all I can to help you.

答应了就要做到。

A promise is a promise.