I heard Messenger of Allah ﷺ saying, "The swearing (by the seller) may persuade the buyer to purchase the goods but that will be deprived of Allah's blessing."  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ الْحَلِفُ مُنَفِّقَةٌ لِلسِّلْعَةِ مُمْحِقَةٌ لِلْبَرَكَةِ