why didn't portia trust bassanio in act 3 scene 2
Or, if the question regards Portia's speech that begins "You see me, Lord Bassanio, where I stand," A MIDSUMMER NIGHT's DREAM, even a plot summary, can be interesting.
If you mean that she fears that he might choose the wrong casket, we find that in Act 1, scene 2, most of the other suitors say that they are leaving Belmont unless Portia "may be won by some other sort than your father's imposition, depending on the caskets"(1.2.90 or so). It seems that others fear the "riddling contest"(Bevington). One might recall the Friar's comment in ROMEO AND JULIET: "Be plain, good son, and homely in thy drift. / Riddling confession finds but riddling shrift"(ROM2.3.55 or so).