Why doesn't Big Ma take Cassie's adivce to move to the farm wagon forward where customers will notice it?

THis is because they are in a town dominated by white people. They can't draw attention to themselves in any way. They can't be perceived as undercutting "white" produce or overstepping they place. Ma knows that this is unfair but reality dictates they do what is necessary to keep their land and hence a greater dignity.

Graziano (a.k.a. Gratiano) and Narissa

While Bassanio was busy falling for Portia, Graziano had his "eye" on Portia's woman in waiting. Notice the parallelism in the second and third lines of this passage? Parallelism is the similarity of structure in a pair or series of related words, phrases, or clauses: "You saw" / "I beheld" ; "You loved" / "I loved." This nifty little technique emphasizes the fact that Graziano's engagement to Nerissa mirrors, or parallels, Bassanio's engagement to Portia.

So why does Shakespeare orchestrate this double wedding? Well, it seems like Graziano and Nerissa's hookup says a lot about Bassanio's relationship with Portia and the nature of love and marriage in general. When Graziano makes his big announcement and admits that Nerissa only agreed to marry him if Bassanio won the casket contest, the couples' abrupt declaration of "love" doesn't exactly seem very genuine. Same goes for Bassanio and Portia, whose marriage is fuelled, in the beginning, by Bassanio's desire for Portia's money.

Graziano's behavior seems to copycat Bassanio's later in the play, too. Bassanio gives away Portia's ring after the trial, and Graziano gives away Nerissa's ring (4.2). Read more about this in "Symbols." Nerissa is also a very practical girl. Hmm. This must be why she agrees to marry Graziano if Bassanio can win Portia.

Please ignore the second reply, it belongs to a different question.