Racketeer? Because of that I FINALLY understand the significance of Nitram's name. It took me this long to see something right in front of my eyes... Please, never stop speaking the English language because you make it so much fun to read. I love it! 
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Don't give somebody a system to abuse. Even someone who hits himself over the head when he simply thinks of influencing his character OOC would be tempted to use such a thievery system with poor judgment. And either way, SOMEBODY is going to complain. Didn't Konstantin receive "thievery gloves" from a GM and everybody complained ceaselessly, groaning over how unfair it was that he RPed a thief well enough that he received a bonus item? I mean, just look at Ultima Online and how they treated the thievery system: thieves stole whatever they wanted and whenever they wanted, so everyone complained until the Devs implemented Trammel, the "safe world," for all victims of thievery to hide - causing the thieves to complain in turn. Either way, someone's going to be unhappy. You win a little, lose a lot I'm afraid.
You know that thievery can still be RPed; you stated that. So what's the problem? Just be creative! The system IS built for thievery. As far as I know, since I haven't visited in a while, trading is still done by simply dropping an item on the ground and trusting your fellow traders to pay for it without running away. I stole a firesword back in the day while playing on my halfling; I simply took it without paying and ran for the hills with little more than a "#me bags the sword and bolts away as fast as his little legs can carry him." The town guard was called and everything - it was so much fun! So, while you're telling us that a thief needs to think on his feet and be creative, there's a simple answer - one of many - to your "problem." This is one of the reasons that "safe trading" hasn't been implemented, after all... (or has it? I better go check ingame before I make myself look like a doof.)