very collectible Lugers mostly
My impression is the ATF is much more uptight about handguns going through C&R then anything else. If you order a bunch of Nagant revolvers or something the dealer who sells them is requested to inform the ATFE, or so I have heard. Buy a few crates of K31s and no one cares.
ATFE agents probably don't know enough about the value of different handguns to tell which might be used in a crime and which might not.