The biographies of Muhammad that I am reading talk only generally about it being problematic to be an orphan. They mention very few specifics. There seems to have been a stigma about orphans, but the biographies are not clear on the nature of the stigma, what people actually thought about orphans that was stigmatic. Also, there is some talk of his uncle Abu Talib being unable to divide his sons' inheritance with Muhammad. But I don't see how that would matter: in the mercantile environment of Mecca, couldn't an enterprising young man like Muhammad have built up his own fortune with the caravans?
In the Qur'an, Muhammad frequently admonishes guardians not to misuse the inheritance of orphans, but he himself had no inheritance that could have been misused (or very little -- one account says his father was able to leave him a couple of camels and a slave girl). Also it seems very unlikely that Abu Talib would have misused any inheritance belonging to Muhammad. So I'm guessing that his stress on managing orphans' inheritance properly had more to do with seeing other orphans being cheated rather than himself.
What exactly were the problems that made life hard for orphans in general, and the orphan Muhammad in particular, in Mecca?