So this is a great question that I have grappled with on the rare occasions that I have used a private DM.
My dive operator in Cozumel provides complete valet diving and typically has, on average, 4 divers to a DM. Those divers generally tip anywhere from $10-15 per tank to be divided between the DM and the captain
I’m not sure if the private DM rate is actually shared with the DM. I assumed that DMs make most of their money from tips which is why I felt obliged to tip close to the equivalent of what the DM would have gotten leading a group of 4 divers. This makes a private DM very pricey.
Have I been grossly over paying?