A man came to the Prophet ﷺ and said, "I am often betrayed in bargaining." The Prophet ﷺ advised him, "When you buy something, say (to the seller), 'No deception." The man used to say so afterwards. (Using translation from Bukhārī 2407)

رَجُلٌ لِلنَّبِيِّ ﷺ إِنِّي أُخْدَعُ فِي الْبَيْعِ فَقَالَ إِذَا بَايَعْتَ فَقُلْ لَا خِلَابَةَ فَكَانَ الرَّجُلُ يَقُولُهُ