What is the ruling on taking a percentage for debt collection, paid by the debtor to the collector upon final settlement?

It is not permissible for the creditor to stipulate that the debtor repay more than the original debt, as this is explicit usury by the consensus of scholars. However, if an affluent debtor procrastinates in repayment, he is obligated to repay the debt and bear the costs of its collection, such as the lawyer's fees and the fees of entities utilized by the court, provided that these fees are determined according to customary rates and not as a percentage of the money.