Anyone who claims to be a messenger of god can ONLY be assessed by what they themselves claim is the message.
No, they can never be assessed by their claims because anybody can make claims. They can only be assessed by what they actually do. As Jesus said "Ye shall know them by their fruits."
Proofs of Prophethood
Bahá’u’lláh asked no one to accept His statements and His tokens blindly. On the contrary, He put in the very forefront of His teachings emphatic warnings against blind acceptance of authority, and urged all to open their eyes and ears, and use their own judgement, independently and fearlessly, in order to ascertain the truth. He enjoined the fullest investigation and never concealed Himself, offering, as the supreme proofs of His Prophethood, His words and works and their effects in transforming the lives and characters of men. The
tests He proposed are the same as those laid down by His great predecessors. Moses said:—
When a prophet speaketh in the name of the Lord, if the thing follow not, nor come to pass, that is the thing which the Lord hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.—Deut. xviii, 22.
Christ put His
test just as plainly, and appealed to it in proof of His own claim. He said:—
Beware of false prophets, which come to you in sheep’s clothing, but inwardly they are ravening wolves. Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. … Wherefore by their fruits ye shall know them.—Matt. vii, 15–17, 20
In the chapters that follow, we shall endeavor to show whether Bahá’u’lláh’s claim to Prophethood stands or falls by application of these
tests: whether the things that He had spoken have followed and come to pass, and whether His fruits have been good or evil; in other words, whether His prophecies are being fulfilled and His ordinances established, and whether His lifework has contributed to the education and upliftment of humanity and the betterment of morals, or the contrary.”
Proofs of Prophethood, Bahá’u’lláh and the New Era, pp. 8-9