If the advertise one thing and send another, refund is entirely on them, if its say an OCUK branded 580gtx, AND they added a disclaimer in the product detail saying picture is for illustration purposes only, final cards differ, then theres no legal obligation to provide a specific card, just the correct specs as listed. In general places shouldn't add anything but a picture of the actual card being sent, more than anything because its a lot of hassle if they add the wrong picture.
I haven't checked but as of a few days ago the entire 580gtx's listings were incorrect in half of what they said, misleading and false advertising, incorrect specs and same "speed % advantage" numbers on differening speed cards, which are obviously incorrect.
False advertising is prevelant but it really shouldn't be too hard to push any retailer into a full refund if they made a mistake with the specs.