I believe I've read that, although there are supposed to be adjustments to your p/p skill based on what kind of armor is worn (see page 233 of the manual), these adjustments weren't actually programmed into the game. I could be wrong, though.
It is supposed to be the p/p skill that guides your success at stealing from a merchant. If you can't succeed with Bernard after trying what I detailed above, then I honestly don't know what else you can try. Maybe you just weren't cut out for a life of crime, eh?
