The deferred price may be higher than the cash price, but the chosen price must be fixed when the sale is concluded. Once fixed, it cannot be increased because of default, nor does early payment automatically reduce it.
The important point is certainty at the time of contract. Different options may be discussed beforehand, but once the sale is concluded one definite price must govern the transaction.
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Valid Sale, Deferred-Payment Sale (بيع مؤجل) and Cost-Plus Rules
The deferred price may be higher than the cash price, but the chosen price must be fixed when the sale is concluded. Once fixed, it cannot be increased because of default, nor does early payment automatically reduce it.
The important point is certainty at the time of contract. Different options may be discussed beforehand, but once the sale is concluded one definite price must govern the transaction.