Prepaid labels and QR codes

After a sale we buy a prepaid label with the platform shipping account and email it to the seller, with a QR code for no-printer drop-off when the carrier supports it. The label is also on the seller's order page.
The buyer chooses among the cheapest 1 to 3 USPS or UPS prices.
If live shipping rates are not available, checkout shows that shipping is not connected and an estimate. The seller then adds tracking by hand. That manual tracking is the fallback.