Not so flattering, it seems…
It is not uncommon to hear many a Muslim asserting that long before Muhammad’s prophetic career began he was known among his people as a man of utmost integrity and as having an impeccable character. One will often find these Muslim propagandists claiming that Muhammad’s contemporaries knew that he was an honest man, one in whom there was no falsehood. In fact, they even gave him the moniker Al-Amin, or "The Trustworthy".
The problem with all of these assertions is that they are not based on contemporary eyewitness accounts but on sources which were written centuries after Muhammad’s death. And they were also written at a time when Muslims had the upperhand and could basically rewrite history to their liking. The Muslims were pretty much free to read back into the life of Muhammad their specific theological views and beliefs concerning their prophet.
More importantly, the Muslim scripture itself is a witness against the assertions made by these Muslim apologists. When we analyze the Qur’an we find that the people around Muhammad did not believe that he was the beacon of truth or that he was a completely honest man. Their testimony is rather unflattering, to say the least, and demonstrates that the later stories of Muhammad’s enemies praising his character are nothing more than legend, clear examples of myth-making at its best.
We know indeed that it grieves thee the things they say; yet it is not thee they cry lies to, but the evildoers - it is the signs of God that they deny. S. 6:33 Arberry
And if they call you a liar, say: My work is for me and your work for you; you are clear of what I do and I am clear of what you do. S. 10:41 Shakir
And if they call you a liar, truly apostles before you were called liars, and to Allah are all affairs returned. S. 35:4 Shakir
And when it is said to them, 'What has your Lord sent down?' they say, 'Fairy-tales of the ancients.' S. 16:24 Arberry
And when We change a Verse [of the Qur'an, i.e. cancel (abrogate) its order] in place of another, and Allah knows the best of what He sends down, they (the disbelievers) say: "You (O Muhammad) are but a Muftari! (forger, liar)." Nay, but most of them know not. S. 16:101 Hilali-Khan Nay, they say: "These (revelations of the Qur'an which are inspired to Muhammad) are mixed up false dreams! Nay, he has invented it! Nay, he is a poet! Let him then bring us an Ayah (sign as a proof) like the ones (Prophets) that were sent before (with signs)!" S. 21:5 Hilali-Khan
But the misbelievers say: "Naught is this but a lie which he has forged, and others have helped him at it." In truth it is they who have put forward an iniquity and a falsehood. And they say: "Tales of the ancients, which he has caused to be written: and they are dictated before him morning and evening." Say: "The (Qur'an) was sent down by Him who knows the mystery (that is) in the heavens and the earth: verily He is Oft-Forgiving, Most Merciful." S. 25:4-6 Y. Ali
Was it a wonder to the people that We revealed to a man from among them: 'Warn the people, and give thou good tidings to the believers that they have a sure footing with their Lord'? The unbelievers say, 'This is a manifest sorcerer.' S. 10:2 Arberry When Our Clear Signs are rehearsed to them, they say, "This is only a man who wishes to hinder you from the (worship) which your fathers practised." And they say, "This is only a falsehood invented!" and the Unbelievers say of the Truth when it comes to them, "This is nothing but evident magic!" S. 34:43 Y. Ali
And they (Arab pagans) wonder that a warner (Prophet Muhammad) has come to them from among themselves! And the disbelievers say: "This (Prophet Muhammad) is a sorcerer, a liar. S. 38:4 Hilali-Khan
A Soothsayer and Poet
And (they) said: "Are we going to abandon our aliha (gods) for the sake of a mad poet? S. 37:36 Hilali-Khan
Therefore remind! by thy Lord's blessing thou art not a soothsayer neither possessed. S. 52:29 Arberry Nor is it the word of a soothsayer: little admonition it is ye receive. S. 69:42 Y. Ali
A Madman (Majnun – lit., "jinn-possessed")
And they say: "O you (Muhammad) to whom the Dhikr (the Qur'an) has been sent down! Verily, you are a mad man. Why do you not bring angels to us if you are of the truthful ones?" S. 15:6 Hilali-Khan
Or do they say, 'He is possessed by a ginn?' Nay, he came to them with the truth, and most of them are averse from the truth. S. 23:70 Palmer Then they had turned away from him (Messenger Muhammad) and said: "One (Muhammad) taught (by a human being), a madman!" S. 44:14 Hilali-Khan
To summarize the testimony of the Qur’an, Muhammad’s contemporaries viewed him as
A liar. A forger and plagiarizer. A sorcerer and a magician. A soothsayer and poet. A madman, perhaps as a result of being possessed by jinn, i.e. demon-possessed.
Now since Muslims believe that the Qur’an is a contemporary account that was composed during Muhammad’s lifetime they must contend with the fact that the so-called earliest Islamic source which they possess does not support the claim that the pagans of Mecca viewed Muhammad as a trustworthy person. If anything, the statements of the Muslim scripture imply the very opposite, that Muhammad’s contemporaries considered him to be a liar and deceiver, one who was prone to make stories up, passing off tales of the ancients as revelations from God. This explains why they didn’t believe him when he said that God was speaking to him. They saw this as just another one of his far-fetched stories, more of his fantasies and allusions, and viewed this as one of his attempts of trying to make himself someone important with the hopes that his people would take him seriously this time and submit to his wishes and desires.
Moreover, it will not help Muslim to simply dismiss the statements of the disbelievers on the grounds that they are nothing more than false assertions and allegations since this only exposes the blatant inconsistency of Muslim polemicists. Keep in mind that it is the Muslim propagandist who is appealing to the assertions of the disbelievers to prove that Muhammad was a trustworthy person. S/he cannot therefore simply discredit the claims of the unbelievers when they are unflattering to the character of Muhammad. After all, if their testimony is reliable enough to support of Muhammad’s integrity then by the same token the unbelievers’ claims are also good enough to call his character into question. The Muslims cannot have their cake and eat it too.