Frames are other story, of course, if you want Ray Ban you pay for (Luxottica-owned) Ray Ban. But, again, a lot of dirt-cheap non-name frames but, also, local-produced high-quality ones are available (cheaper than Ray Ban, much more expensive than no-name).
I know, that Luxottica owns all brands which will be sold to you in Tax-free shop or in in-flight magazine, but still.
For me there is one problem: Luxottica bought Oakley. Best technical sun shades ever. Now owned by Luxottica :-(
About ordering on-line: good to you if you can wear random frame without pain in nose bridge and ears :-( I don't need prescription glasses, but I've spent a lot of time to buy shades for cycling - something, which seems Ok in shop is painful after 8 hours of wearing for me.