He agrees to do jobs such as writing, translating and designing, then he hires someone else to do them

There is a difference between a person selling what he does
not possess of goods and items, and making a contract to do some work, which
may be hiring or requesting manufacture. In the latter two cases it is
permissible for a person to agree to carry out a particular task, then to
make an agreement with someone who will do it for less pay, so that he may
take the difference, unless that agreement is for the first worker to
undertake the work himself, or he was chosen deliberately, because of some
particular distinction that he has that the one who hired him wants from
that worker himself, such as one who hires a well-known calligrapher or
designer.

It says in Kashshaaf al-Qinaa‘ (3/566): If the hired
worker agrees to do some work in return for payment, such as sewing a
garment and the like, there is nothing wrong with him giving the work to
someone else for less than the fee he charged. End quote.

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: If
a person is hired to do a task, such as if it is said to him: We want you to
clean this house every day, and you will have one hundred riyals a month,
then he in turn hires someone to clean the house every day, according to the
same agreement, but for fifty riyals, that is permissible.

This is how people operate nowadays. You will find a
government, for example, agreeing with a company to clean the mosques, each
mosque for such and such per month, then this company brings workers who do
what they have agreed to, for less than a quarter of what the company agreed
to with the government.

But if there is a reason why the one who hired a specific
person wants that person to do the job himself, this is not permissible. For
example, if you hire someone to copy out Zaad al-Mustaqni‘ [a book of
Hanbali fiqh] for you, and you know that this man’s handwriting is good, and
that he makes few mistakes, then he hires someone else whose handwriting is
beautiful, and he will write it for less than you hired the first man, then
the scholars say: This is not permissible, because what matters in the case
of copying is not only the beauty of the handwriting; rather it is the
beauty of the handwriting plus punctuation, diacritical marks, vowels and so
on. How many people there are whose handwriting is the most beautiful of
handwriting, but they lack precision; they write the verse “ghayr
il-maghdoobi ‘alayhim wa la’d-daalleen (ot
of those who have evoked [Your] anger or of those who are astray)”
[al-Faatihah 1:7]
incorrectly. Many students have beautiful handwriting, but when it comes to
precision they have no knowledge of the rules of the language; many other
people have bad handwriting, and no one can read it except one who is used
to it, but when it comes to the rules of writing, they excel. Whatever the
case, what matters is that when a person is hired for a specific reason
(such as a skill that only he possesses), it is not permissible to let
someone else take his place.

End quote from ash-Sharh al-Mumti‘ (10/39).

A similar distinction is made between selling a particular
item that a person does not possess, and selling an item that meets a
specific description, which is what is known as bay‘ as-salam
[salam transaction; payment in
advance]. This is an
exception from the prohibition on selling what one does not possess. Please
see the answer to question no.
184816.

But your question has to do with hiring. It is permissible
for you to offer to write, translate, design and so on, and to make an
agreement on specific fees and work, then to hire someone to do that work,
unless the customer wants you to do the work yourself.

And Allah
knows best.