There's a fellow here in town who buys a large number of proof and mint sets each year and submits them, unopened, to NGC for certification. According to him, he makes a nice profit by doing this just because he hits on the PF70 and high mint state coins. Not sure if this is "book" profit or if he's actually selling them and making money. It costs quite a bit to sell a large number of slabbed coins and lots do ok but from what I've seen the lot prices produce fairly low dollars per coin, especially for PR69DCAM common type stuff.