How can the up selling skills affect positively or negatively on both firm & customer?

offcourse it will affects positive if you doing that the number of customer or the income of the company will be increase. because in upselling you given idea to the costumer for example you have a promotion or something new  some customer dont know about it but you come to the customer and tell some details i think the customer will be happy and surprise  and they will think to buy ..