1. The seller should be truthful to the purchaser and should not deceive him or lie to him regarding the quality of the product, the amount it cost him, etc.
عن أبي سعيد رضي الله عنه عن النبي صلى الله عليه و سلم قال التاجر الصدوق الأمين مع النبيين والصديقين والشهداء (سنن الترمذي رقم 1209)
Hazrat Abu Sa’eed Khudri (radhiyallahu ‘anhu) reports that Rasulullah (sallallahu ‘alaihi wasallam) said, “The trader who is completely honest and trustworthy will be (resurrected) with the Ambiyaa (‘alaihimus salaam), the siddeeqeen and the martyrs (on the Day of Qiyaamah).”