First off, it is quite clear that the narrator wants to draw an implicit connection between the two Sinbads. The connection may be taken in such a way as to produce a before and after effect: the porter being the former, the lord being the latter. Hence, the similarity in their names is no coincidence.
The narrator describes the porter's hardships lucidly:
a poor man who earned his living by carrying burdens upon his head ... a heavy load under the sweltering heat of the summer sun ... sat to rest a while wiping away the sweat that trickled down his forehead [1, p. 113]When the porter noticed the splendid house, he was amazed. He, however, kept on with his duty and was going to start out again after his rest, when the page caught his attention and implored the porter to come inside. The porter, being a hardworking individual, which is implied here, declined with the excuse that he had to get back to work. After some more discussion, the porter was persuaded.
The lord explicity states, ``Presently, my brother, you shall hear the tale of my fortunes and all the hardships that I have suffered before I rose to my present state and became the lord...''[1, p. 114, emphasis added]
In each tale, the lord finds himself deserted by his shipmates, either left for dead, or through the destruction of his merchant ship. For example, in the first voyage the lord and his merchant companions land on a strange black island, soon to find out that it is a large whale. The lord does not make it back to the ship on time, and it leaves without him. In most stories, he clings to a piece of wood until he reaches land. He then suffers some hardship on land, such as in the fifth voyage, when he encounters the Old Man of the Sea, who enslaves him as a man would a horse or donkey. Then due to some ingenious plan of his, which would, under normal circumstances be considered blasphemous or sinful under the Moslem religion, such as in the forth voyage where he kills for food the men of those women who die before their husbands and are entombed together as was the custom in that land, he survives the ordeal bringing with him the riches from whence he came. After the recounting of each tale, the lord gives the porter a hundred pieces of gold and sends him home.
The porter's endurance of hardships are not explicitly announced throughout the stories. However, they are first announced at the beginning of the story. The fact that the porter's getting one hundred pieces of gold each time is a testament towards his hard work (long overdue.) By the end of the seventh story, the porter now is a ``constant'' fixture and seven hundred pieces of gold richer. The narrator does not say whether the porter continues to receive gold after each visit, however, the seven hundred pieces are more than enough to make this once poor porter very rich.