PayPal does not print letter rates - only package rates
Stamps.com prints any rate

The 98 or 99 cent rate does not include tracking, so if you use it for a PayPal or Ebay transaction the recipient need only say "I didn't get it" and the money is taken from the seller's account without delay.

If 95% of parcels get to their destination, what happens to the other 5%? Is that good customer service? Do customers end up paying postage due?