Is it obligatory to pay a designer who provided a poor service without a prior agreement on the price?

If the questioner stipulates knowing the wage before work begins, then the contract of hire (ijara) is not concluded except by agreement upon it. If an agreement is not reached, then the questioner has the right to return the work without paying anything, or to accept it and pay the customary wage (ujrat al-mithl) as determined by experts. This is based on the hadith: "Whoever hires a worker, let him inform him of his wage."