وَمَنْ أَطْلَقَ الثَّمَنَ فِي الْبَيْعِ كَانَ عَلَى غَالِبِ نَقْدِ الْبَلَدِ.
Translation: An unqualified price is interpreted by reference to the locality’s predominant currency.
When a locality has one predominantly used currency, an unqualified numerical price can be interpreted in light of that commercial custom.
At a local shop where “500” unmistakably means 500 Pakistani rupees, the understood currency may be sufficiently identified.
This turns on established practice and context, not on a universal rule that numbers always mean the same currency.