how should I respond to this?

That's great that you mentioned when the demand increases, quality and consistency can decrease. With the price ceiling set the demand will significantly increase because more and more people will be able to afford the product. This can cause companies to quickly put out new or existing product out with no regard to the actual quality of a product. I also agree, a weight loss product should not have a price ceiling but instead be determined by the demand of the consumer. When the product is in high demand prices should go up, when not in demand prices should go down.