What does the USPS verification do?

Clicking on the Verify USPS addressicon calls the USPS web page to verify the address. While this verification is not of course 100% accurate, it does catch and correct the following errors:

In addition, if known, it will inform you of the following errors:

It will also provide the zip+4 address. The USPS does use a number of abbreviations and normalizations so the generated address may look different than the supplied address. For instance "Street" is turned into "ST" and most directions such as "North" are turned into "N". These normalizations are not required for the successful delivery of your item.

While this does not guarantee the address is correct, it does do a number of checks that can catch typo's or other invalid or incomplete information.