Selling above MRP and MRP tampering is very common in Amazon. But in this case there is a chance that Xiaomi maybe selling the filter below MRP and Amazon is selling at MRP. Only way is to check the actual product packaging.
From January it's mandatory to display the product MRP in e-commerce sites.
Another annoying thing which I saw with amazon is the way they handle lightening deals, Real price is 1999 and lightening deal price is 1998 Rs and then they show that deal got claimed 70 percent, How is that possible?
someone mentioned on reddit that this is done when they have amazon pay offer on lightning deals. so unless the product is put in lightening deal, you would not get amazon pay cashback. but you are right, this happens even when there is no amazon pay cashback deal going on.