For a genuinely faulty item covered under warranty, the customer should not bear any expense in returning the item... sure things happen, but the customer paid a fixed amount for a product guaranteed to work (or be repaired or replaced) for a set period of time so it's not reasonable for the customer to be out of pocket in this situation.
If the customer returns an item as faulty and it turns out to be perfectly fine (possibly awkward as some faults are intermittent)... then I think it's fair for the customer to front the postage cost both ways and maybe even a contribution toward the testing.
Most retailers and manufacturers I have dealt with to-date have gone by the "normal" means (although it depends on what the item is) which is that the customer returns it and then the manu/retailer sends it back... I'm kinda OK with that as most don't usually charge if you make a mistake and the item isn't really faulty, some do charge for the extra shipping cost however. So it might be a reasonable balance that's most reasonable on all parties.
A few, exceptional, retailers and manufacturers will even cover the cost of postage both ways. I've known OcUK to do this too, but that may have only been because them item was practically DOA, rather than 18 months down the line.
I normally purchase from OcUK, sometimes one yellow competitor for ore business-orientated items that OcUK don't stock or I'll visit an electronics retailer in Switzerland thanks to my location. For example, my 2x Titan X cards came from OcUK and were shipped straight to me here in France. Annoyingly for me, they are both Gigabyte
The R9 280X in question did not come from OcUK... otherwise I would probably be returning it to them at the moment.
You can get very cheap postal services, I know... I just think it's insulting and unacceptable for a manufacturer to put the cost of shipping both ways onto a customer for a device that should not even have a fault (yeah, I know... things happen... but they're a multi-million pound company and I'm a home user).