He would have gone bust trying to sell everyone on Beta instead of VHS.
"Please vote to preserve the unique character of Warren…" - Robert Duvall

None of them struck me as particularly smart (an understatement), including Jack with his delusions of artistry.
"facts are stupid things" Ronald Reagan

It helps me!
That scene is so funny. The grin on his face as he bops along to that banjo music.

Go ahead and groove with it!
DISPLAY thy breasts, my Julia!

I would have bought a stereo from him! When he drops the mic with "I think you need all that bass", I was sold!

I'm not sure how smart Buck is. Even without the deleted scene where Buck is talking about sound equipment in the van, you can tell from his first scene in the stereo store that he really has no idea what he's talking about. But he's a good guy and he may end up being successful with his stereo store because he seems like a salesman you could trust.
DISPLAY thy breasts, my Julia!

and I think his boss at the stereo store is saying the same thing!!

I don't think he's smart and I don't think he's supposed to be very smart.
He's a good person (they're all good people in their own way, they just have demons) who throughout the film does nothing that would make you dislike him. In this world of drugs and mayhem he's one of the only ones who abstains. Yeah, he's part of the industry, but you never see him doing drugs, you never see him in a bad light. THe worst thing you can say about him is that he has no fashion sense, but he's at his core a good person. That's why he ultimately ends up in such a great situation. It's the directors way of rewarding the guy who deserves it. It's a happy ending for the guy who may not be very smart, but is a good person.

He was also the smartest of the performers. Jack was smarter than he was but of the performers Buck beat them all. Plus he had ambition and some skill outside of his acting. On top of that he was not a bad person and not a shallow person. He tried to act that way but it did not work for him. You can tell at the New Year's party how miserable he was. He was smart enough to know that pretending to be someone was not nearly as awesome as just being someone.