M doesn’t look especially like D but it can be quite lovely in it’s own right. The presumption that less color is ‘better’ is a matter of taste for the customer to decide. Have you seen this stone? Do you love it?
I agree that the depth figure is a bit suspicious. I’m also always nervous to see a thin girdle on a princess. Princess cuts can be quiite fragile and this makes it even worse. Don’t buy this without a professional opinion from someone who can actually see the stone and specifically ask about the durability of the stone.
As a completely unrelated observation, I’ve noticed that it’s a good sign when a dealer describes a stone as an M. Why? Because the worst misgradings that walk in my door are stones that are sold as I-J that are actually M-N. When a dealer calls it an M, this is usually the case. The stone is what it is; however the dealer chooses to describe it. If they call it an M, and price it like an M then everybody can walk away happy. It’s when they call it an I and give you a ‘deal’ that there starts to be a problem.