Where there is no fixed judgement, the traditions and conventions of community are to be referred

وَقَالَ شُرَيْحٌ لِلْغَزَّالِينَ سُنَّتُكُمْ بَيْنَكُمْ رِبْحًا. وَقَالَ عَبْدُ الْوَهَّابِ عَنْ أَيُّوبَ عَنْ مُحَمَّدٍ لاَ بَأْسَ الْعَشَرَةُ بِأَحَدَ عَشَرَ، وَيَأْخُذُ لِلنَّفَقَةِ رِبْحًا. وَقَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لِهِنْدٍ: «خُذِي مَا يَكْفِيكِ وَوَلَدَكِ بِالْمَعْرُوفِ». وَقَالَ تَعَالَى: {وَمَنْ كَانَ فَقِيرًا فَلْيَأْكُلْ بِالْمَعْرُوفِ} وَاكْتَرَى الْحَسَنُ مِنْ عَبْدِ اللَّهِ بْنِ مِرْدَاسٍ حِمَارًا، فَقَالَ بِكَمْ قَالَ بِدَانَقَيْنِ. فَرَكِبَهُ، ثُمَّ جَاءَ مَرَّةً أُخْرَى، فَقَالَ الْحِمَارَ الْحِمَارَ. فَرَكِبَهُ، وَلَمْ يُشَارِطْهُ، فَبَعَثَ إِلَيْهِ بِنِصْفِ دِرْهَمٍ.Shuraih told the weavers, “You are permitted to follow your own conventions to solve your problems (it is legal for you to stick to your traditions in bargain).” Narrated ‘Abdul Wahab: Ayyub said he heard from Muhammad who said, “There is no harm in selling for eleven what you buy for ten, and you are allowed to take a profit for expenses.” The Prophet ﷺ told Hind, “Take what is reasonable and sufficient for you and your sons.” Allah تعالى says: “Whoever is poor, can eat (from the orphan's property) what is just and reasonable (according to his labours).” (V.4:6) Al-Hasan hired a donkey from ‘Abdullah bin Mirdas and asked him about the hire. The latter replied that it was for two Daniq (a Daniq equals 1/6th Dirham). So Al-Hasan rode away. Another time, Al-Hasan came to ‘Abdullah bin Mirdas and asked him to hire the donkey to him and rode away without asking him about the hire, but he sent him half a Dirham.