Looks like paypal provides postage payment services that wold probably work with USPS pickups. I saw no indications that it's limited to paypal buyers.

https://www.paypal.com/shipping

A How-to

http://www.dummies.com/how-to/content/ho...

You print out the postage (either Click N Ship or if selling on eBay, print shipping label from My eBay).

Then you leave the packages in your box.

I really need to find out how to ship packages from my house. I use padded envelopes to ship my products. Has to be paypal to pay for the shipping costs. Thank you! Help would be GREATLY appreciated! (I'm a equestrian business)