Price of import = sale price of items (or fair value) + shipping ACTUAL cost. The amount you were charged for shipping was possibly less than it actually cost to ship, meaning the declared value comes out higher. + exchange variations.
That's a lie. You are to be charged on the value you PAID for. You cannot be taxed anywhere in the world for something you didn't pay, regardless of the company eating the shipping price or not. And Bitmain doesn't decrease the actual shipping price. If anything they increase it.
Well, they don't steal anything, they don't get anything more from this, so yeah they often mess up the value on things, i'm not sure why, but its a pain to deal with the rectifying the price declared.
They get 17% from chinese government out of everything they export, or what they say they do.