Call for Artists, Making Money at Juried Art Fairs, Craft Shows and Festivals
I don't think double matting is worth it. There are many photographers who have had this kind of discussion with themselves, and with others on this forum, and many have said that customers will often just throw out the mat anyway; it's real purpose is to temporarily make your images look good in the hand. So, if you double mat, and the above-mentioned theory is true, you'd be throwing away that much MORE money.
I'm still in the process of testing the idea that no mats at all is even better. I use wide corner mounts and mount my prints to oversized 8-ply mat board. The goal in doing this is to give the image some room to "breathe", and somewhat resemble a matted print, without spending the money on the mat itself. The jury is still out.