If I catch anyone touching my gear except to help me don/doff it between dives...
On a serious note, I have had conversations with other divers on this topic. A couple have had thier tank valves turned off after pressurizing the system, valves backed off too far, etc only to find out the problem AFTER entering the water. The boats I use for my trips to the Islands do not touch the valves on divers' gear. In fact, they tell us during the briefing we get when we get to the first dive site, is that if we need a fill, THE DIVER is responsible to remove the first stage and replace it. I always make sure that fill was done, my hoses, and if I walk away from my gear, I double check it before donning it for the next dive and of course, do the buddy check as well, and the DM checks just before the giant stride into the water.
The diver is awlays responsible for his/her own gear. If you need someone to set your gear up for you, even if you ar eon a full-service boat...imho, you have no business being a diver.