The Prophet ﷺ forbade a town-dweller from selling on behalf of a desert-dweller, even if he were his father or his brother.
أخبرنا محمد بن بشار قال حدثني محمد بن الزبرقان قال حدثنا يونس بن عبيد عن الحسن
أن النبي ﷺ نهى أن يبيع حاضر لباد وإن كان أباه أو أخاه
[Sahih]. Abu Dawud narrated it in Kitab al-Buyu, in the chapter on the prohibition of a town dweller selling on behalf of a nomad, hadith no. 3440, from the hadith of Yunus with this wording. It is also found in Sunan al-Kubra, hadith no. 6083. See the following hadith, as it serves as a corroborating witness for it.