"...Supposing the situation that a non-dealer ships a firearm to a buyer's FFL (dealer), and that, for whatever reason (failed to pass, chooses to return, never shows up!) the firearm is still the buyer's property, correct?..."
The firearm once it reaches the FFL is considered 'transfered' to that FFL, no longer the sellers gun. It is logged in as 'Acquired From' (sellers name/address,ect) in the FFl's log book. The only way it can go anywhere ('Disposition')is to another FFL (w/copy of their FFL) or to another non-FFL (with 4473/NICS done).
Doesn't matter if it was sent/dropped off for consignment sale or sent for xfer to another customer or sold outright to the FFL.
If the firearm is refused, background check failed, or for whatever reason the gun doesn't get transfered to the local customer,,the FFL cannot simply box it back up and send it back to the original seller(non-FFL).
That's one of the problems you get in to. It has to go to another FFL in the sellers state for transfer (4473.NICS) back to the seller.
Again it seems out of wack, but that's the regs.
Selling to C&R license holders,,sure will any day of the week.
Either FTF or ship it to them. Same deal as an 01 or 02,