I think the marker spray comes out in the tanning process but dont quote me on that!! I go for the largest skins, which have a nice shape, no bald patches and a good even covering of wool. If you are getting late into the season (winter!) give the wool a good tug, if it comes away from the skin then its no good. Check the underside of the skin, if there has been any flystrike or the lamb has been injured in anyway you will see damage to the skin, that is no good. Also, take care when handling at slaughter, the same goes for the meat quality, lambs handled by pulling on the wool not only damages the meat but also the skin.
Just give Devonia a ring, you can either deliver to them or post, depending on where you are!! I just ring up and tell them i have posted for example 4 skins, 2 black and 2 white. I always try and vacumn pack the skins in a bin liner, pushing out as much air so they get smaller and smaller! then double bag them again in bin liners, then put in a postage plastic bag.