Is it permissible to impose a percentage of the profits of a workshop that has been sold but its full price has not yet been paid?

It is not permissible to take a percentage of the shop's profits after its sale. Debtors must pay the remaining debt when it becomes due if they are solvent, as the Prophet (peace be upon him) said: "Delay by a rich person is oppression." If they are insolvent, they must be granted respite until a time of ease, as Allah Almighty says: "And if there is one in [financial] difficulty, then [give him] time until a time of ease." It is not permissible to obligate them to pay a percentage or anything extra beyond the agreed-upon price if they delay payment. If the payment due date arrives and they are solvent but do not pay, the creditor may take their case to court to claim his right.