It should be totally different from extort. I think it should be like a level 35 or so skill that requires you to type something like shoplift beef.butcher that way it is your own choice whether to shoplift something. If you fail the butcher would catch you and either attack you (but those things hit hard that is why it should be a high level skill) or the butcher kicks you out of the store for like 25 tics.
Just a thought, because I think a truely Master thief should be able to steal from a butcher just like I could steal from you without you having the slightist idea.