I ship them rolled in tubes, print side out, acid free tissue more than covering the print, the roll then wrapped in kraft paper so that it can be easily removed from the tube. Labeled 'open other end' at the bottom. I run strips of paper (usually Canson Rag trimmings) about half an inch wide from the bottom forming a loop at the top, though the middle of the roll so that the paper roll can be pulled from the tube. I pad the top and bottom caps. I use 4" tubes up to 34" print width. 6" for larger prints.
I wouldn't advise Print Shield, Hahnemuhle Protective Spray, Moab Desert Varnish or any other lacquer based coating if you are shipping rolled. They are all too brittle and you will get surface cracking when unrolling; whether you see it then or not.
I have never had to resend a print so far.
Shipping flat is great for the client, but you need to create a box, and watch out for oversize fees.
Brian A