To be honest 老实说
To be honest, I just don't want to go.
说心里话,我真不想去。
To be honest, I am disappointed at you.
说实话,我对你很失望。
To tell the truth 说实话
To tell the truth, I don't agree with you.
真格的,我不同意你的意见。
To be candid with you 坦白的说
To be candid with you, I think you're making a dreadful mistake.
跟你说实话,我觉得你在犯一个可怕的错误。