The prohibition of the town-dweller selling on behalf of a bedouin Sahih Muslim 1521
Translation
Ibn 'Abbas (Allah be pleased with them) reported Allah's Messenger (ﷺ) as saying
The riders (carrying merchandise) should not be met in the way, and townsman should not sell for a man of the desert. The narrator reported. I said to Ibn 'Abbas: What do these words really imply-" The townsman for the man of the desert"? He said: That he should work as a broker on his behalf.