They are FFLs. They will ship via USPS to your FFL.
As a nonFFL, you can only ship long guns via FFL.
If you are going to ship a gun, use shipmygun.com. It will give you the best rate via UPS overnight. It's set up with most FFLs already in their database.
You need to make sure your buyer's FFL will accept from an individual. Some do not.
I usually ask my buyer to have their FFL either send me a copy of their FFL or give me the first part and last part of the number and I can go online and verify through ATF that the FFL is still active.
If the buyer won't give you an FFL and wants you to ship direct to them, that's illegal. Not sure how it is within the same state that have face to face laws, but different states require FFL transfer