I hear your concerns. Nevertheless, countless others have done it (sending PPs via courier with tracking and delivery receipts) and have received their PPs in return with no issues.
If the instructions refer you to use a VAC, heed the instructions, send via VFS/VAC - then the VAC does have an agreement with CIC to ensure the safe return of the PPs to the applicant.
If it just says to send via courier, get a reputable and well-established courier who has tracking and delivery receipts. Find a courier, call them and discuss your concerns and how they can ensure the delivery of the PPs.
.../atb