Shipping from an FFL to an FFL. I have received handguns, long guns, receivers, shipping next day air, 2nd day air, and even ground.....

UPS specifies all handguns go Next Day Service, long guns don't matter.

FEDEX specifies all handguns go Next Day Service, long guns don't matter.

USPS specifies licensees only can ship handguns, long guns don't matter.

How are dealers getting aways with shipping using different methods? What kind of liability is there?

Shipping rules for firearms apply federally for USPS, the rest is corporate.  If you are shipping UPS or FEDEX and break their rules then you "MAY" get banned(?) from them but that's it, Although I have not heard of any issues with private (corporate) shipping rules being broken, or even checked.

Just follow the ATF guidelines (USPS) and you should be cool.

The same way people cheat on their taxes......they ain't been caught yet.

Violate USPS regs.....Felony.
Violate UPS or FedEx tariffs......at most they cancel your account, hit your account with fees for the level of service you should have used, hold your package until they damn well feel like delivering it.

Perfect, thank you!