Is the lawyer's earning unlawful if he defends a guilty person and seeks their acquittal, and are there Islamic conditions for the legal profession?

If advocacy is to protect evil, it is forbidden. If it is to protect good, it is praiseworthy and commanded. The lawyer must study the case before undertaking it; if justice is with the one seeking advocacy, then he should support him. But if he has no right, then the lawyer must prevent him from injustice by clarifying the invalidity of his claim until he is convinced and abandons it.