Clearly Vinted prioritizes the return solution, giving the seller the choice whether or not to cover the return costs. If you opt for the buyer to pay for the return, then this missed transaction will not have cost you anything, so why refuse it?
Accept the return and the matter is closed at no cost to you.
Accepting the return is often the least risky (and least conflict-prone) solution, and by charging the buyer, it often discourages them, and the sale is still finalized. At worst, you get the item back and put it back up for sale.
Vinted’s terms and conditions clearly state that a sizing error on the part of the buyer is not an acceptable reason if it was correctly indicated in the item description.
I took the trouble to measure the insole for this reason.
Vinted handles disputes minimally: they take a minimal commission, which is what makes them successful, and in exchange they provide a minimal service, which is logical.
However, experience shows that it is generally better to reach an agreement with the buyer if possible, rather than relying on Vinted’s arbitration, which is frankly random.
Until now, when I refused returns by explaining that the dimensions and sizes were clearly indicated, buyers understood and finalized them on their own.
This time, after the refusal, they asked for a price reduction. I foolishly thought Vinted would close the case in a few days: following their request, I sent explanations, photos, and screenshots..