Costing is something many designers get so, so infuriatingly wrong.
It can be incredibly frustrating if you are a professional maker who relies upon their business to pay their way in life- mortgages, rising bills, etc, when there are other sellers out there barely charging the cost price of the materials because it is their hobby and not something they rely upon. It devalues the industry as a whole and it doesn’t make them popular with those trying to forge a genuine business.