My seller client has an executed contract with a buyer. After the buyer completed his inspection during the option period, the buyer asked my client to make several repairs and to use a repairman the buyer chose. My client agreed to complete the repairs, but does he have to agree to use the buyer’s repairman?

No. TREC contracts require the seller to complete the agreed repairs before closing, but the contracts don’t provide for the buyer to designate who makes the repairs. 

Note that the Completion of Repairs and Treatments Paragraph in TREC contracts requires the seller to either use someone who is licensed to make the repairs or, if no license is required by law, the seller must use someone who is commercially engaged in the trade of providing such repairs—unless the buyer and seller agree otherwise in writing. 

This doesn’t mean a seller can never use an unlicensed handyman for electrical repairs. It means the seller must use a licensed electrician unless there is a written agreement between the buyer and seller to use that unlicensed handyman for electrical repairs.