IMO that would really be depending on the expectations of condition... I mean, how bad really was the damage? Like severe bending, separation of the cardboard? Did your buyer have a suggestion? Depending on if you sold them at a reasonable price - greeks seem a bit fickle with some moonstone and sunlight only 150-250 range when they used to be a hundred more on average that if it were me I would maybe comp the postage costs which would be 20ish so like 10% ish range?? That's just my opinion, see what your buyer says and look to work it out because it also seems they wanted a break on customs fees, well that's the price for not having insurance in some sense. Hoping your buyer is reasonable as you seem like a really reasonable seller to work to offer a refund for rough handling out of your control