Customer must give instructions in writing

BIFA (2005) Section 11. A
No Insurance will be effected except upon express instructions given in writing by the Customer and all Insurances effected by the Company are subject to the usual exceptions and conditions of the Policies of the Insurance Company or Underwriters taking the risk.

CIFFA Section 13 (A)
The Customer must give the Company instructions in writing to arrange insurance on its goods a reasonable time before the tender of goods for storage or transport. 

FIATA Model Rules Section 3.
Insurance
No insurance will be effected by the Freight Forwarder, except upon express instructions given in writing by the Customer.

NCBFAA Section 8.
Insurance. 
Unless requested to do so in writing and confirmed to Customer in writing, Company is under no obligation to procure insurance on Customer's behalf; in all cases, Customer shall pay all premiums and costs in connection with procuring requested insurance.