Since I'm working on a couple of papers on Sextus' Pyrrhonism, I've reread Michael Williams' "Scepticism Without Theory", The Review of Metaphysics 41 (1988): 547-588. It's a fine article, so if you have access to that issue of the journal, I highly recommend that you take a look at it.
Williams argues that the Pyrrhonist has no theoretical or epistemological commitments, which explains why ancient Pyrrhonism, unlike modern and contemporary forms of skepticism, is not based upon a few general skeptical arguments, but applies the "method of opposition" to particular conflicts. This also explains why the Pyrrhonist restricts himself to reporting what has happened to him so far and goes on investigating, instead of claiming that knowledge or apprehension is impossible. Like myself, you will probably ask "What about the Modes of Agrippa? Aren't they general epistemological arguments?" According to Williams, the Agrippan Modes do not ground or explain the Pyrrhonian method of opposition but "instantiate it within epistemology" (p. 579). That is to say, the Pyrrhonist employs those Modes, not because he is committed to them, but only to counter the Dogmatists' epistemological theories, thereby inducing suspension of judgment. This is, of course, just a sketch of the paper, in which Williams also attempts to identify the reasons for the difference between Pyrrhonism and post-Cartesian skepticism.