When all else fails, go to website, read directions.
As I am sure you are aware, legally a reciever IS the firearm. Everything else is parts. To transfer ownership of a firearm across a state line, it must be sent TO a FFL holder in the home state of the recipient. Does NOT need to come FROM a FFL holder.
Tips on setting up auction- GOOD pictures, GOOD description. Do NOT put hem up as a Reserve Auction- a LOT of folks skip those. Set the lowest price you would take, start them at that price, let it go. State how much your shipping costs will be (not this "actual shipping" crap) STATE in the narrative that you are NOT a FFL, be sure the receiving dealer will accept shipment from a Non-FFL (perfectly legal, some won't) State that you will include a copy of your driver's license (so dealer can log it in to his bound book) Pack well, lotsa padding.
The recieving dealer does not need to send you a copy of his license- he can provide you with his license numbers. You can go online and verify thru ATF EZ Check system. Ship to the address on the license.