Fact is nothing to do with what you believe or what I believe. Fact remains fact whether anybody believes or not. For example there is country called "Lesotho" which might be heard by very few people. Just becuase nobody has heard about it, does not mean that that country does not exist.
Now coming back to prophet's (pbuh) trusthworthy topic, Prophet(bpuh) was not only shepherd but later he became a merchant well before his marriage (I hope you do not disagree with this). let me give an example. I donno whether you have purchased any products online. If you purchase online, you can find seller ratings rated by consumers. When we purchase, we usually try to buy products from highest rated seller. Same thing applies to prophet(pbuh) too. If he would have been a cheater or lier (God forbid) in his business deals, then Arabs at that time would have rated him as cheater and a lier and he would not have been qualified as prophet at all. So, this well proves that, he had been rated by Arabs that he was indeed trustworthy. Check out this text from wikipedia
"Born to %u2018Abdu%u2019llah ibn %u2018Abdu%u2019l-Muttalib, Muhammad initially adopted the occupation of a shepherd, and later became a merchant. In his youth, he was called by the nickname "Al-Amin" (Arabic: %u0627%u0644%u0627%u0645%u064A%u0646 ), a common Arab name meaning "faithful, trustworthy" and was sought out as an impartial arbitrator" http://en.wikipedia.org/wiki/Muhammad#Overview
So, it's fact that he was trustworthy. This refutes your claim that there is no proof that Arabs at that time called him trustworthy.
