Is selling government bonds or checks outside of banks for more than their original price to facilitate procedures considered usury (riba)?

Selling checks and bonds for cash is not permissible, because it is an exchange with deferred payment, and thus does not fulfill the conditions of immediate possession and equality when the genus is the same, or immediate possession when the genus differs. The Sharia-compliant solution is for the client to appoint the bond seller as his agent to buy the bonds for him from the bank for a known fee.