Need to verify that the FFL you are sending your firearm to is legit? Verify!
https://www.atfonline.gov/fflezcheck/There has been a rash of Armslist / CL scammers trying to buy your weapons and have them ship it to "their" FFL, but they provide a fraudulent FFL document. The BATFE provides you an easy online FFL verification site to make sure you are sending your firearms to the real deal.