From what I've read and seen, you'll have to work pretty hard to get the ATF after you for this. I'm pretty sure it was outlined that selling large quantities from a deceased relative is fine and downsizing a collection is fine. What gets you into trouble is if you're buying the same firearm multiple times and selling it privately.
There's always that chance they could go after you for a single sale, but it's pretty much like worrying about a cop giving you a speeding ticket for going 56 in a 55.
There's always that chance they could go after you for a single sale, but it's pretty much like worrying about a cop giving you a speeding ticket for going 56 in a 55.