Ibn Abī al-ʿIzz (رحمه الله) said[1]—and these words are derived from the writings of Ibn Taymiyyah such as al-Nubuwwāt:
Prophethood is only claimed by the most truthful of the truthful or the most lying of the liars, and this (affair) is not confusing except to the most ignorant of the ignorant. Rather, the circumstances of their states of being reveal (their truthful or lying nature) and are known by way of them. There are numerous ways to distinguish between the truthful and the liar in (affairs that are) less than the claim of prophethood, so how about a claim of prophethood itself.
From the many affairs that indicate the truthfulness of the Prophet (صلى الله عليه وسلم) and which are easily recognisable upon simple reflection, except to the most ignorant of the ignorant are the following:
01 Given that the one who falsely claims prophethood has to be the greatest of liars, with the greatest type of lie, then he can only be doing so for something he deems great in the world, otherwise, he would not make great the lie. This is usually fame, power, authority, riches and other worldly desires. However we do not see any sign of this in the Prophet Muḥammad (صلى الله عليه وسلم), and he was offered riches, authority and women to compromise his call, but he refused and lived a life of poverty right until his death.
02 The greater the lie, the harder it is to sustain, especially over a lifetime, or a good part thereof, as the inconsistencies and contradictions would reveal themselves over time. However, the Prophet (صلى الله عليه وسلم) was known as the truthful and trustworthy before Islām, and after the call to Islām, his truthfulness was more evident.
03 The greater the lie, the more the liar is willing to compromise in order to gain followers with ease. However, the Prophet (صلى الله عليه وسلم) ordered with what were strict observances and condemned the unjust practices that the society was steeped in. Establishing prayer, giving charity, raising females and not killing them at birth, prohibiting interest, intoxicants, fornication and many other affairs that require mental and physical toil and sacrifice.
04 The greater the lie, the more fearful the liar would be of being caught out, and thus, he would not make challenges that could falsify his claim immediately. He challenged the Arabs to produce what is like the Qurʾān, if they thought it was not from Allāh. He declared that his uncle, Abū Lahab would never accept Islām and die a polytheist. These and other statements would jeopardise his call.
05 Had the Prophet (صلى الله عليه وسلم) lied about receiving revelation, then the only knowledge he would have to present would be from the heritage and history of the Arabs and details of major events, wars, lineages and so on. And we do not find any of that in the Qurʾān. There are no extensive details about himself, his lineage, his birth and upbringing, his family and children, which would be expected. No names are explicitly mentioned of his companions and closest friends prior to Islām and after Islām , with one exception (Zayd). One would expect lots of names, facts, information and details from the past and present lived experience, but that is not the case.
06 Had the Prophet (صلى الله عليه وسلم) lied about receiving revelation, his speech would have been ordinary speech recognised by the Arabs or like the poetry that they were masters in. However, the Qurʾān was unlike anything they had heard, or could imitate, as has preceded.
07 Had the Prophet (صلى الله عليه وسلم) lied about revelation, he would not have made so many prophecies which were fulfilled and continued to be fulfilled after him. He would have known that failed prophecies would have led people to abandon his message straight away, and his call would never endure for long, and be cut off and be forgotten in a matter of years after him.
08 Had the Prophet (صلى الله عليه وسلم) been a liar, this would manifest in his conduct and behaviour, for it is from the signs of liars and hypocrites that they tell lies, cannot be trusted, break their promisese and behave with ill-manners. Because lying leads to wickedness and truthfulness leads to righteousness, then in the character of the Prophet (صلى الله عليه وسلم) we see the most dignified, lofty character, and that can only be an indication of being truthful, not its opposite.
There are many other considerations in addition to the above, they are just for the purposes of illustrating that only the most ignorant of the ignorant would be unable to discern the true and false claimant to prophethood and fail to see the truthfulness of the Prophet Muḥammad (صلى الله عليه وسلم).