A question about appointing a lawyer to collect property rents: Is it permissible to determine his fees as 10% of the collected rents, given that their value is not known beforehand, and are the costs of judicial notices and legal expenses included in this percentage or separate from it?

"The 'Ju'al' (stipulated payment) is money committed for a work that is not an 'Ijarah' (lease/hire contract). The majority of scholars stipulate that the 'Ju'al' must be known, but some have permitted ambiguity if it does not prevent delivery. Accordingly, it is permissible for a lawyer's fee to be a percentage of what he obtains from cases, because this ambiguity does not prevent delivery. Legal expenses and notices can be included in the 'Ju'alah' contract, with the possibility of agreeing that the client bears the legal expenses while the lawyer receives the agreed-upon percentage."