His friends ask him to buy computers for them and he adds a profit for himself

I am a computer and network engineer, and I work with several
companies and individuals, buying computers and accessories for them.
Sometimes customers come to me, and they may be some of my
acquaintances, wanting to buy computers and accessories etc. I tell
them how much the equipment will cost them and I include my commission
in the price without them knowing that I have added the commission.
For example, a computer may cost 2000 riyals, but I tell them that it
will cost them 2500 riyals; I buy the computer with my own money then
I receive 2500 riyals from the customer or the person after they
receivethe computer. My question is: is this transaction valid, in
which I take commissionfrom them without themrealising? Please note
that I deal with the companies that sell the computers and the invoice
from the company shows 2500 riyals when the price is really 2000
riyals. Please note that I state the specifications of the computer
and the time of delivery, and I deal with the customer on the basis of
sincerity. What is the Islamic ruling on that?.
Praise be to Allaah.
It is permissible for you to buy the computers that the customers
want,then to sell them to themwith an appropriate profit, on condition
that you take possession of the computer first, before you sell it to
the customer, because the Prophet (blessings and peace of Allah be
upon him) forbade selling thatwhich one does not possess.
An-Nasaa'i (4613), Abu Dawood (3503) and at-Tirmidhi (1232) narrated
that Hakeem ibn Hizaam said: I asked the Prophet (blessings and peace
of Allah be upon him): O Messenger of Allah, sometimes a man comes to
me and asks me to sell him something that I do not have, so I sell it
to him then I buy it for him from the market. He said: "Do not sell
that which you do not possess."
The hadeeth was classedas saheeh by al-Albaani in Saheeh an-Nasaa'i.
The customer should also be aware that you are selling and you are not
just volunteering to look for a computer for him; but it is not
stipulated that he shouldknow the amount of your profit. Rather if he
describes the specifications that he wants, you should tell him that
you will sell thiscomputer to him, if you bring it for him, for such
and such an amount.
But if you have volunteered to look for acomputer and buy it for
someone, then you do not have the right to increase the price of the
computer.
Shaykh Ibn 'Uthaymeen (may Allah have mercy on him) said:
If an individual has set himself up to do work, then someone comes to
him and gives him fabricand says: Sew a garmentfor me, then he has the
right to take payment for that, because he set himself up to do work.
But if he did not set himself up to do work, then he does not have the
right to take anything, because the other person gave it to him on the
basis that he was doing him a favour.
So anyone who does thejob for another person without a contract is
notentitled to any payment, except in three cases:
1. Saving the property of one who is protected in sharee'ah from destruction
2. returning a runaway slave
3. if a person has set himself up for work.
End quote from ash-Sharh al-Mumti', 10/88
There are two other cases in which it is permissible:
1. If you are not the seller; rather you are an agent working for
a fixed wage. In that case you should tell the customer that you will
buy the computer for him for a better price than can be found in
themarket, and that in addition to that you are entitled to a specific
amount in return for your research and meeting the specifications that
he wants;
2. if you are an agent working on commission,such as if you will
receive 10%, for example, of the price of the computer.
In these two cases you do not have the right to take anything more
thanthat which has been agreed upon, and any discounts or free gifts
that come with the computer belong to the one who appointed you to buy
it, and you shouldnot take anything of them.And Allah knows best.