What you are seeing from the responses is that the answer to your question is, 'It varies, from LDS to LDS.' I started DM because I wanted to improve my skills, not because I wanted to teach, or assist in the shop. I found out how much I enjoyed working with OW students and am now continuing my 'development'. As a DMC, I was a scut puppy. I hauled tanks, helped students get their gear from the locker, even towed the shop gear trailer to the quarry for checkouts, etc., etc. We joke about slavery and indentured servitude, but there are no unreasonable expectations, and our DMCs are treated with courtesy, respect and professionalism. I also got to demo skills, lead tours, etc. Our internships were not time-referenced, as much as experience-referenced. DMCs were expected to participate in / assist with one full OW class, one full AOW class, and one Rescue class. If we wanted to DMC for specialty classes in addition, we were welcome to do so. No pay as a DMC, of course. And, we did pay tuition for the DM course. As a certified DM I became part of the shop 'staff'. I now sign up to do Scuba Reviews, to DM for OW, AOW and Rescue classes - i.e. to do what I am allowed to do by my certification, and I get paid for it (minimal, but pay nonetheless). I get shop discounts on the basis of being shop staff. I can 'market' Scuba Reviews, Discover Scuba courses, etc. as vigorously as I choose (and the shop owner is delighted to have me do so), although it is for and through the shop, not just for me as a completely independent contractor. If we have a shop coastal charter scheduled, I may be asked to join the group to be available to assist the group leader (in which case my charter fee is comp'd), or to 'lead' the group (charter fee comp'd + minimal extra compensation). The bottom line, there is no requirement of service, beyond DM certification. It is anticipated that many of those who complete DM will want to serve as shop staff in some capacity, but there is no obligation to do so, any more than there is any obligation on the part of the shop to use your services.