A case of sale (ba’i) in which the buyer doesn’t haggle over the price (i.e., takes it as a given). The buyer acts in such a manner based on a specific positive trait in the seller such as trust, straightforwardness, reliability, etc. Ba’i al-mustarsil may also involve a buyer who is unaware of the actual price of an item in a way that enables the seller to exploit his lack of knowledge, i.e., information asymmetry, by increasing the price above the prevailing market price. The “unsuspecting” buyer will be willing to buy at the price quoted by the seller. As such, the sale is said to be associated with al-ghubn (al-ghaban).

Ba’i al-mustarsil may also refer to a sale transaction in which an unknowledgeable farmer brings his produce to the market and sells it at a price lower than the prevailing price. This sale suffers from information asymmetry which the seller, unaware of market conditions, is blamed for.

Based on ijtihad, ba’i al-mustarsil is viewed by shari’a scholars either as an ordinary contract of sale, and as such is subject to the general rules of contracts (regardless of al-ghubn it is associated with) or as a distinct contract of sale, like ba’i al-najash and talaqqi al-rukban, and hence is subject to specific rules and precepts and produces its own legal effects and considerations. In the first view, the contract is still binding (lazim), irrespective of any price discrepancies. Al-mustarsil, accordingly, has no khiyar (option) to return the object of sale and recover the price. In the second view, a contract that is associated with istirsal (unawareness of the actual price) involves a great amount of ghubn and exploitation (to which al-mustarsil or the unknowledgeable party is exposed). In this respect, some fuqaha opined that ghubn al-mustarsil is tantamount to riba, and therefore, it is haram or forbidden by shari’a. The second opinion gets more traction among shari’a scholars.

Ba’i al-mustarsil is also known as ba’i al-isti’man or ba’i al-istislam.