If you open the box, according to other threads, then it can't be sold as new so you'd loose some of the refund.
Why should the customer loose out either?
Your forgetting that the customer is buying an item they haven't actually inspected themselves, especially if it is from an etailer. This is fine if it's something like a memory USB stick, heat sink or even an SSD hard drive but its a totally different kettle of fish with a GPU, monitor and potentially a CPU.
Would you call up a garage, order a car, pay the money and take delivery without seeing the car in person or taking the car for a test drive?
This is the problem I have. It's all very well changing the rules to stop retailers getting stung by idiots and people who flaunt the previous DSR law (I agree with that part) - returning items if they don't overclock well - but when the changes are basically open to wild guidelines and the potential of holding back up to 25% to restock an item, an item which had to be installed or setup to test, it's a bit daft.
It could be seen as though DSR favoured the customer but this system has swung totally the other way and has put people buying online in a pretty naff position tbh.