Er.. no. I never buy used, nor do I lend or borrow harmonicas for the simple reason that I'm a bit choosy what I put in my mouth. I asked my GP once whether a rather persistent chest infection I was suffering from could be down to re-infection from playing, and he was of the opinion that it would be unlikely for germs to live long enough outside the body to be a problem, but not impossible. I also suffer from occasional cold-sores which are ragingly infectious and it wouldn't be kind to inflict that on anyone else. Remember, enthusiastic playing, a long gig or a slightly damaged cover plate can easily open up a cut on your lip, and that's inviting problems.