Paypal and USPS prices

Question

If I use paypal to print out addresses for my packages for ebay, how do I determine how much to charge for a certain package? For example, If I sell something to like a Zone 4 location, and it weights 12 ounces, I know what the cost will be by looking at the post office website.I have my own scale at home. But what if the scale is off and the price I print from paypal is under or over the amount I paid? How does the post office know to give you the money back or a debt slip saying I owe them money. I was not too clear at how this worked.

Answer 1

If you don't put enough postage on the package, the post office will send it back to you for Insufficient Postage and you'll have to remail it,

If you put too much postage on, the post office will deliver it and not say a word to you. You won't get your money back.