No postal scale. No account. That's another account I neither want, nor need. I don't sell enough knives to justify fooling with a USPS pre-paid account. We're not talking high volume here--just the occasional knife.
Also, the do-it-yourself system at the PO seems to be clunky when you want to add things like insurance and delivery confirmation. I don't know for sure, but I wonder if the online version is similar.
You ought to check out USPS online. It really is a piece of cake and it's pay as you go. It's not a prepaid deal.
The PO will give you the boxes, they give you the tape ...(in fact, they send the tape / boxes etc directly to your house after you place an order for same at USPS.com.) You can do the insurance, delivery confirmation, or whatever on line. An individual package with insurance takes just minutes to address. When you do it electronically, you also get free electronic delivery confirmation on every Priority package addresserd online. I finally broke down and bought a scale after years of over guessing on weight.
Once you start doing it at home, you'll never stand in line again.