Different agencies have different standards for designations by the same name. I'm a NAUI instructor, and was in fact at one time a NAUI Master Diver. In the NAUI system it's a real course ... made so not through the purchase of specialty classes, but by course content specific to a Master Diver class and designated skills mandated for that level fo diving. In other words, you don't just send them $50 and receive the badge. In the NAUI system, Master Diver is the diving skills portion of their DM designation ... so it does exactly what you indicate some people want ... provide a path to pursue the diving skills of a pro without having to deal with the leadership and liability issues. SEI has a similar Master Diver designation based on the requirements of the old YMCA program from which they were created. Other agencies may, as well ... but I'm not familiar with the specifics of those agencies.... Bob (Grateful Diver)