problems returning item through USPS

I had an item to return and didn't want to use the pre-paid label.. mainly because of the cost, but also the QVC returns center is about an hour from my house and if I use their label is goes through three different states to get back to here (which seems so crazy and not very carbon friendly).

Anyway if the item is under say $30 I don't insure it but send it with a delivery confirmation. I get to the counter today and asked for this but I was told that QVC only accepts parcels with the delivery confirmation if you choose insurance or a signature something. In other words they don't want you to have the ability to return something with a tracking number that's cheaper than they offer (which it would be if I sent it 1st class with the delivery confirmation).

But my problem with this is how can a private company dictate to the Post Office what thier customers can and can't do? And this was no mistake. The counter clerk couldn't process a delivery confirmaion as it was blocked to that specific address (QVC's return address).

Has anyone else come across this?