'Free shipping' is a sales gimmick. It really means 'shipping included'. In some countries, the products are so cheap and their postal services so affordable that they can offer this 'free shipping' internationally and still make a profit.
Whereas a country like the UK, where Royal Mail rates are comparatively high internationally, you won't see a lot of 'free shipping' offered on international orders.
Obviously nothing rides for free, so your iphone case probably has a manufacturing cost of a buck and a half, if that, and it will cost very little for the Asian seller to mail it to you. It will take about 3-4 weeks to arrive.
As for who pays, - ultimately the buyer. How the total amount gets divided is up to the seller. Some sellers have tried that 'free shipping' thing here but Canada Post rates are so high it makes the sellers' items appear too expensive. Besides, I think most people prefer an honest and affordable shipping rate when they buy, - even if that fee really is £42 to mail their items.
