When someone says they "had their doubts," it typically means that they were uncertain or skeptical about something. Some synonyms for this phrase include: hesitated, second-guessed, conflicted, vacillating, undecided, apprehensive, skeptical, unsure, wavering, and uncertain. These words all convey a sense of hesitation or uncertainty about a particular situation, decision, or idea. It's important to note that having doubts doesn't necessarily mean that something is definitively wrong or bad, but rather that there is a level of reservation or caution in one's thinking or approach. Using these synonyms can help add nuance and variety to one's language while still conveying the same core meaning.