I have purchased many miners from Bitmain, S1 and S2. Never has one appeared to have seen any use. In fact, they were so clean and unscarred I wondered if they had even been functionally tested. But I have yet to have ever had a DOA or failure of any kind.
Indeed, same experience. But perhaps the last miners that they sold for 0,4xx BTC where used in BITMAIN's farm...