What constitutes a naive buyer (al-mustarsil)?

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Al-Mustarsil is defined by Imam Ahmad as one who does not know how to haggle in trade (mumakasa). In another narration, it means one who does not haggle. Essentially, the person defers to the seller, accepting the price without bargaining or recognizing the overcharge. Conversely, one who is aware of the possibility of overcharging or who would have known had they waited, and rushes the transaction resulting in ghabn, has no option to revoke, as this is based on their own failure to exercise caution.