You can turn a return down at either point — before it's sent, or after it's arrived and you've looked at it. The button is on the page in both states.
Say why
The reason box is emailed to the customer, so write it for them, not for yourself: "outside our 30-day window" or "the sleeves were used" tells them something. It's kept on the return afterwards, so in three months you can still see what was decided and why.
It's optional, and leaving it blank sends a bare refusal. Don't — a declined return with no reason is the thing that turns into a bad review.
The two moments differ
The email says which situation it is, because they're very different to receive:
- Declined up front — "we've reviewed your request and can't accept it". They still have the goods, and they've spent nothing.
- Declined after it arrived — "we've looked at the items you sent back and can't refund them". They've paid postage and you're holding their property, so expect a reply. Sort out getting it back to them.
What it doesn't do
No money moves and no stock changes. Declining is a decision, recorded — and there's no un-decline, so if it was a mistake, refund the order directly instead.
Two of you at once
If a colleague has already decided this return, your press is refused with "This return has already been actioned" rather than deciding it twice. Reload and you'll see what they did.