ANSWER:

If you are an agent to your supplier and you only take commission from him after selling the products, you must not add anything for your benefit. 

But if you are the actual seller and you buy products and then sell them after possessing them, you can add whatever profit you want. 

Do not lie! Tell them that I will sell you such products after I possess them for so and so. 

QUESTION: I do small time perfume business. I take orders from customers and engage my supplier in another country. The customers sometimes ask – “can you check how much your supplier sells a certain perfume for” that I did not advertise. If I quote a value higher than the supplier, to earn a profit, is this considered lying?