Black Pastel are variable
This girl IS a black pastel but yet looks like a Cinny, now how do I know for sure she is a Black Pastel? I produced her from Black Pastel to Normal pairing I hatched 4 Black Pastels from that clutch and she is the only one that look this way.
Above is the sire that produced her with one of her sibling.
If someone (the seller) tells you it is a Black Pastel there is no reason why you should not believe this person, there is not much to gain from trying pass a Black Pastel as a Cinny or vice versa