"Honest-to-god" is a common colloquialism used to emphasize the truthfulness or sincerity of a statement. However, there are various synonyms that can be used to express a similar sentiment. For example, "genuinely," "truly," "sincerely," "authentically," and "in all honesty" can be employed to assert the veracity of a statement. Alternately, use phrases such as "hand on heart," "cross my heart," or "swear on my life" to convey a strong sense of honesty. These expressions can be effective for driving home the point that you are being truthful, transparent, and upfront with the listener or reader.