One or two files could be cherry picked, although even then they might tell you enough...; I'd prefer something like "Could I please glance at your code base?" ... but only after I got enough experience to recognize tells at roughly a glance.

Even then I'm not sure it would have saved me from the worse code base I ever worked with, the only one I flat out decided had to be replaced (after spending a month fixing some bugs and learning it took days to determine how to safely fix one, the code was so tangled).

In reference to the NDA comments, if a company is too paranoid about that sort of thing without clearly having "special sauce" worth protecting---unfortunately, future products or product directions can also both be worth protecting and necessary to disclose to you---that's a strong sign to avoid them.