Most of this isn’t that mysterious in practice. Apply whatever you know about how supermarkets, bars, and other cash accepting businesses operate. Then add in the fact that yes, drivers would occasionally get robbed, it was a risk of the business and priced in much like shoplifting is for a supermarket.

Yes, payment for “cash/collect on delivery” is made on delivery rather than in advance. If the goods are not paid for, they are returned to the retailer.

American page:

https://faq.usps.com/s/article/Collect-on-Delivery

Canadian page:

https://www.canadapost-postescanada.ca/cpc/en/support/kb/sen...

These days of course you pay electronically on delivery. No actual cash involved. My grocery delivery does that, because the final cost depends on the weight of certain items as well as if I have any old crates or bottles to return.

So on delivery I pay either contactless by NFC or by QR code. Super easy, barely an inconvenience.

I bought things CoD in the days when eBay still did that (90s). The postman would come to your door with the CoD bill and you'd hand over a cashier's check to them, then they'd give you the package.