bucketofchicken, sorry about you not being able to see the guest post author on the current mobile app. Tech are working on a new one as we speak - in the meantime, the mobile site (rather than the app) displays them better.
Guest posts are a way of showcasing a variety of voices on the site, whether that's politicians or public figures we think have something interesting and relevant to say (eg: Marie Stopes' Dawn Purvis, when Bernadette Smyth was sentenced; or Jo Swinson on Shared Parental Leave), or our own bloggers. Very rarely, they might come from large organisations as part of a commercial partnership, but we'd always make it clear if that were the case.
More often, guest posts are from 'ordinary' Mumsnet bloggers and, we hope, highlight issues which might affect or interest MNers (eg: Tuesday's guest post on Pathological Avoidance Demand Syndrome). Sometimes the guest poster approaches us, and other times we spot something that we think will make a good one, and approach them ourselves.
Guest posters do occasionally respond to questions on the thread off their own bat (as with Tuesday's post) - thanks for the feedback, though, we'll try and encourage them to do so more often (though obviously we can't make them do so!).
These are all relevant questions, so what we'll do is put a page up on site explaining how we do things, and link to it from future guest posts.