[Umayrr]

Assalmualaikum, I am from Mauritius island,and my name is Umayrr.I live precisely in Curepipe, and home number : 230 6705606.
My father has a bookshop (selling school accessories and books) which he owned since 12 years, this year he is intending to sell it to another person. The months of December, January and February are the peak months where the bookshop works at its best. My father already evaluated all the contents of the bookshop at cost price.
The new owner wants to take the business before the peak months (in November, i.e one month before peak months) .The evaluating cost of the bookshop is about 450,000 rupees, and so, based on our previous records, the bookshop can get a profit of about 225,000 rupees in the peak months. As previously mentioned, the evaluation of the bookshop was done on cost price, which means that my father is not getting any profit from the sale of the bookshop. So my question is that is my father allowed to charge a reasonable profit upon the cost price? If yes? How will he calculate that amount?
Jazakallah khair,hope to get an answer very soon Insha Allah.