Shack Keys

Those two keys can only be obtained (Or unlocked, whatever) with specific perks. The shack in front of the Scrapyard will be opened if you get the "Contract Killer" Perk. There, you can sell the ears of good characters you have killed for caps.

The Shack north of the Wheaton Armory will be unlocked if you get the "Lawbringer" perk. There, you can sell the fingers of evil characters you've killed. Both are kinda lame perks, as the ears and fingers don't sell for much. I suggest just ignoring the perks. Don't sweat over the shacks.

I disagree. The "Lawbringer" perk racked me up a lot of caps. Maybe not as much as going around selling every item I come across, but I did make good money. The "Contract Killer" perk might not get you as much caps because I believe there are less good NPCs in the game than there are bad/evil. Of course I could be wrong though. Since the level cap raises to 30 with the Broken Steel expansion, it wouldn't really be a waste to pick up one of those perks. I personally like "Lawbringer" more, but choose whichever you want, if you want one at all.