Narrated Tawus from Ibn 'Abbas (RA), Allah's Messenger (ﷺ) said:

"Do not go out to meet riders (to conduct business with them), and a city-dweller must not sell for a man from the desert." I asked Ibn 'Abbas (RA), "What did he mean by 'A city-dweller must not sell for a man from the desert.'" He replied, "He should not act as a broker for him." [Agreed upon and the wording is al-Bukhari's].

وَعَنْ طَاوُسٍ, عَنِ اِبْنِ عَبَّاسٍ ‏-رَضِيَ اَللَّهُ عَنْهُمَا‏- قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ لَا تَلَقَّوْا اَلرُّكْبَانَ, وَلَا يَبِيعُ حَاضِرٌ لِبَادٍ ".‏ قُلْتُ لِابْنِ عَبَّاسٍ: مَا قَوْلُهُ: " وَلَا يَبِيعُ حَاضِرٌ لِبَادٍ? " قَالَ: لَا يَكُونُ لَهُ سِمْسَارًا } مُتَّفَقٌ عَلَيْهِ وَاللَّفْظُ لِلْبُخَارِيِّ [1]‏ .‏