Hi there. I’m trying to run an experiment with ACKS, and I need the thief to be accepted a bit more neutrally as the experiment deals with ethics, and I don’t need to cloud their judgments out of the gate. I already know I’ll change the Pick Pockets skill to Sleigh of Hand to remove the obvious criminal bent to the ability, but I cannot come up with a name for the Thief. Rogue isn’t any better. I need a name that conveys their interesting skillset or maybe their more opportunistic fighting style without making them sound like bad guy material. Thanks.
Expert. Specialist. Secret Agent. Ninja.
Did you ever play Final Fantasy 6 (3 in the states), the theif Locke had a pretty good take on it: “Hey! Call me a treasure hunter, or I’ll rip your lungs out!”
I like Treasure (or Fortune) Hunter, or perhaps Knave or Trickster if they’re going to be doing sleight of hand type stuff. Maybe a Wrangler or a Beguiler? Mountebank? I’m really stretching here. 
I second the earlier notions. I'll also add "Tomb Raider" "Bravo" "Scout" "Operative" "Prowler" and "Spy"
“[T]here is a mark on this door - the usual one in the trade, or used to be. Burglar wants a good job, plenty of Excitement and reasonable Reward, that’s how it is usually read. You can say Expert Treasure-hunter instead of Burglar if you like.” – Gloin, The Hobbit
You guys are great. Thanks so much. And yes, I played FF6; fun times. ^^ Normally I’d go with Treasure Hunter (2 good sources can’t be bad), but with my experiment suggesting that the party is the king’s special investigation team, I’ll probably go with scout or agent. Thanks again!
Late to the party, but I’ll throw in Long John Silver’s “Gentleman of Fortune”.
I came up with a number of templates when I drafted my version of the thief or “expert” class, the Collector (http://www.autarch.co/forums/house-rules/custom-class-collector). I found that a specialization or focus made them sound more legitimate.
Spell Keeper
Cartographer
Zoologist
Gossipmonger
Game Hunter
Monster Wrangler
Raider
Grave Robber
Heistman
Slaver
Chronicler
Librarian
Plunderer
Anthropologist
Broker of Souls
Agent/Spy
Gemologist
Jeweler
Numismatist
Botanist
Polyamorist
BECMI did something similar, and called the class the “Rake”, in one of the Gazeteers, though I forget which (Dawn of the Empires?).