Is there any discount for the purchase of 3 iPhone X units? And there are also iPhone X devices considered used because they have open packaging and discounts for buying them. ?

What you see are people buying for the whole family for the same price without discount, you can find a used iphone only outside an official Apple store

Discount does not have, but there are some stores that sell used iPhone

There is no quantity discount. I know that ... As for the open box, etc. I would not be able to say, but they would probably exchange the boxes.