This has developed into a really interesting discussion!
Not wishing to cast doubt over individual's honesty, I wonder how many of these "part-time" couriers have notified their insurance providers.
Another issue seems to be the differing charges and systems used by mail-order companies. Kaleidoscope uses Hermes and charges £3.95 delivery but returns are free if courier collects or you take to one of their appointed outlets (One-Stop, BP Petrol Station, Co-op Convenience Store, etc). QVC delivery charges are variable, but they charge for returns via Hermes. Amazon has option to collect from local Post Office, I've used it and it works fine.
Again not trying to stereo-type in any way, there may be a higher turnover of "part-time" couriers given that they are mums, pensioners or others supplementing their income.