What is the religious ruling concerning the fee for legal services, and does a prior agreement with the client make a high fee permissible?

The contract is the law of the contracting parties, unless it violates the Sharia (definition), and there is nothing in it that specifies the amount of profits in commutative contracts such as sale and lease. This is what was decided by the International Islamic Fiqh Academy and affirmed by Sheikh Ibn Baz. There is no difference between sale and lease in this regard, as leasing is the sale of services and selling is the sale of goods, and the prices of services and goods are governed by the system of supply and demand. It is desirable for a Muslim to be gentle with people and to consider their circumstances. If the exaggeration of workers or the depreciation of employers causes harm to the public interest, the guardian (ruler) may intervene in pricing wages. All of this is if the lawyer adheres to the legitimate controls of advocacy, otherwise, compensation for forbidden acts is not permissible.