Question: Is it valid to buy something if one only has a rough idea of the price?
Wa alaykum assalam wa rahmatullahi wa barakatuh,
Thank you for your important question.
It is valid to buy something if only one has a rough idea of what the price is if such items are normally bought. (Ihya Ulum al Din, Ghazali; Sharh Yaqut al Nafis, Shatiri)
Although it is principle invalid because the Prophet forbade vague contracts, it is valid because the fact it is conventional practice compensates for the lack of clarity.
Regarding buying an item that belongs to endowment (waqf), that is not valid. You should check to see if the item actually belonged to the endowment or not.
I pray this helps.
Checked and Approved by Shaykh Faraz Rabbani
Ustadh Farid Dingle has completed extensive years of study in the sciences of the Arabic language and the various Islamic Sciences. During his studies, he also earned a CIFE Certificate in Islamic Finance. Over the years, he has developed a masterful ability to craft lessons that help non-Arabic speakers gain a deep understanding of the language. He currently teaches courses in the Arabic Language.