Who pays for shipping an item is refunded?

I won an auction for a piece of clothing and once it arrived I reached out to the seller straight away and nicely explained that the item isn't in the condition they described. They offered a refund (which I accepted), and they said they wish they just kept the item, so I said I'd happily return it to them too if they paid for shipping. They have since paid me and I realised it was only the amount that I initially sent them (i.e. shipping one way and the item). This means they didn't refund me for the initial cost of shipping. So I'll be sending an item back, and $7.50 down. I do get that if they pay me for shipping they will $15 down, but they'll still get the item back and they should have described it better, because I paid $32.50 all up, and if i was that item even for $4 in an op shop in the condition it was in I wouldn't buy it.

TLDR - if an item is refunded because it's in bad condition, should the buyer or the selling be the one who has to pay for shipping, I.e. should the seller refund the shipping price too?