Product.cs

public class Product : Entity, IAggregateRoot
{
    public string Name { get; private set; }
    public decimal Price { get; private set; }

    public Product(string name, decimal price)
    {
        Name = name;
        Price = price;
    }

    public void SetName(string name)
    {
        Name = name;
    }

    public void SetPrice(decimal price)
    {
        Price = price;
        if (!new ProductNegativePriceSpecification().IsSatisfied(this))
        {
            throw new DomainException("Product Price must be greater than zero.");
        }
    }
}

public class ProductNegativePriceSpecification
{
    public bool IsSatisfied(Product entity)
    {
        return entity.Price > 0;
    }
}