Why an intact device fetches disproportionately more
When a device has a defect, buy-back services and private buyers do not just deduct the repair cost, they deduct a lot more. After all, they have to price in the risk that something else is broken too.
A cracked display therefore often lowers the price by more than the replacement costs. That difference is exactly your gain if you have it repaired first.
On top of that, only a working device can reach the better condition grades at all. Many buy-back portals sort broken devices into a separate category that pays much less.
