To OP.
Now you have listed a laptop for 40,000 rupees, which is $660ish US dollar. Without any information on the brand, model, and whole sale price, it is hard to come up with profit margin. You could be making 50% profit if you can get it for $500 and then resell for $750. But only if no one else around you is selling that same laptop for less. You should do research yourself. Check the stores in the area and compare their prices, then see if you can find out the cost of the laptop if you get it directly from the maker (HP/Samsung), or through a middleman.