Maybe I'm being unfair, but somehow I suspect this will make him seem like a nobleman trying to be a commoner.

That's exactly what this lame disguise is going to look like. Note too that he doesn't make any effort to talk like a commoner either. They've suddenly all got these stupid phonetically spelled accents. He doesn't.

He even beheaded a slaver to Eragon's consternation! (Slavery, by the way, which never comes up again and only seems to exist in Dras-Leona.)

Until Saint Eragon came and made it all go away forever, naturally.