this was done before and they even said the last s-5's they sold were used.
Every single miner bitmain sells is "used". I think they roi most (maybe all) of their gear in house before they sell them.
Bitmain runs their equipment like crazy, I wouldn't be surprised if one or two arrive DOA. Notice how each batch gets cheaper? That's because every batch is based off how much money they make from them (at least that's my theory). S7 B12 looks too good to be true, i'll hold off on them. No ROI expected anyways, so its basically another used s5 from ebay. No profit, and the only difference is that bitmain probably ran it a lot harder than a regular person would.