General synonyms:
* Gullible
* Trusting
* Naive
* Unsuspecting
* Believable
* Easily persuaded
* Dupable
More formal synonyms:
* Trustful: Emphasizes the positive aspect of being willing to believe.
* Sanguine: Suggests a hopeful and optimistic outlook.
* Impressionable: Implies being easily influenced.
* Uncritical: Emphasizes a lack of judgment or analysis.
Negative synonyms:
* Naive: Implies a lack of experience or sophistication.
* Dupable: Suggests being easily tricked or manipulated.
* Innocent: Can be used sarcastically to indicate a lack of common sense.
The best synonym to use depends on the specific context and the intended meaning.