Praise be to Allah.
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.