Is it permissible to take an advance payment from the client to guarantee rights and cover the broker's penalties in the event the client withdraws from the project, and is it necessary to inform him that I am merely a broker, even though my work involves selecting the type of software and the implementing company?

If the contract is for the development of a software program with clear specifications, a known price, and a defined timeframe, it is a permissible Istisna' (manufacturing contract). You are permitted to enter into another contract with a software company to carry out the work, which is known as parallel Istisna', and it is permissible to take an advance payment from the client without informing them about contracting with another company.

The Sharia Standard No. (11) concerning Istisna' and Parallel Istisna' states:

It is permissible to conclude an Istisna' contract between the institution and the beneficiary (mustasni'). The Istisna' contract is binding on both parties if its conditions are met (clarification of the type, kind, quantity, specifications, known price, and defined deadline). The beneficiary has the option if the manufactured item deviates from the specifications. The manufacturer is not permitted to stipulate exemption from defects. The Istisna' contract is only permissible for items that involve manufacturing. It is permissible to stipulate in the Istisna' contract that the manufacturing must be done by the institution itself, and it does not have the right to entrust the completion to another party. It is permissible to defer the price of the Istisna', pay it in installments, or expedite an advance payment.

As for Parallel Istisna':

It is permissible for the institution, as a beneficiary (mustasni'), to conclude an Istisna' contract with a manufacturer and pay the price in advance, then sell to another party through a parallel Istisna' contract with the same specifications, without linking the two contracts. It is permissible for the institution, as a manufacturer, to conclude an Istisna' contract with a client for a deferred price, and then contract with another manufacturer to purchase from them through a parallel Istisna' with the same specifications for an immediate price, provided that the two contracts are not linked. The institution must bear the owner's liabilities, maintenance costs, and insurance expenses before delivery to the client, and it is not entitled to transfer its obligations with the client to the manufacturer in the parallel Istisna' contract. It is not permissible to link the Istisna' contract and the parallel Istisna', nor is it permissible to be released from delivery in one if delivery does not occur in the other.