You can do both.

Shop wise: In the menu, you have the option to set a margin % for your entire shop.  For example: If you think you want to earn at least 20% margin on each sale, just set your global shop margin to 20%. In such cases, when you are sharing the product 20% extra automatically gets added to the price listed by the supplier. For example, the price of a Sari listed at Rs 1000 will automatically be increased to Rs 1200 when you are sharing it.

Product wise: You can also very easily change product wise margin, both at the time of copying products and at the time of sharing products.  Suppose at the time of sharing or copying a Sari listed at Rs 1000, you feel that it can easily be sold at Rs.2000; you can simply edit the price to Rs.2000.