Buying and Selling is prohibited from the time of first adhan of friday prayer. One should halt trading and business upon the hearing of first adhan of friday prayer as it is haram to do so.
يَـٰٓأَيُّہَا ٱلَّذِينَ ءَامَنُوٓاْ إِذَا نُودِىَ لِلصَّلَوٰةِ مِن يَوۡمِ ٱلۡجُمُعَةِ فَٱسۡعَوۡاْ إِلَىٰ ذِكۡرِ ٱللَّهِ وَذَرُواْ ٱلۡبَيۡعَۚ ذَٲلِكُمۡ خَيۡرٌ۬ لَّكُمۡ إِن كُنتُمۡ تَعۡلَمُونَ
O ye who believe! When the call is heard for the prayer of the day of congregation, haste unto remembrance of Allah and leave your trading. That is better for you if ye did but know. [Surah al-Jumua]