Surrender of BL must only be done if you receive the payment of goods in your bank account, else without that if your surrender BL, importer can collect the goods without the need of any original BL.
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Many times fraud importer also ask the exporter to send a swift message to his bank that "Without doing any procedure kindly release all documentation in favour of the buyer", in such case also importer can clear goods without paying anything on any secured banking payment terms.
So take care.... EXPORTER MUST NOT SURRENDER BL OR MUST NOT SEND ANY UNWANTED SWIFT MESSAGE VIA BANK
Q. What is Swift Message ?
A. Just like whatsapp , it's a legal secured server software which is used by bank to bank to send information. Its full form is Society for Worldwide Interbank Financial Telecommunication