As the title says, I'm starting very basic.

One of my players wants to use the Far Horizons Sourcebook and create a Marshal with a Frontier Justice obligation, however Beyond the Rim was created with the core rulebook in mind.

I don't own a copy of the book myself, but I managed to lay hands on one someone in the group does and I'm reading it.

However, I'm not sure how to reconcile someone in the group being a Smuggler with a Debt obligation to a Hutt and including the Marshall in the campaign.

It's like having a Paladin with a Warlock in D&D. It's hard to justify why they don't just start shooting one another out of the gate.

Suggestions? I don't want to tell this person no because I'm too new to sort this out, but it seems like trouble to me.

Well the martial is a frontier lawman and a local one. Sometimes on the frontier you have to prioritize your concerns and crimes beyond your jurisdiction aren’t your concern. So let’s suppose your lawman is offworld tracking down info on a human trafficking scheme plaguing his settlement. He might figure working with a smuggler is a good way to uncover information. By the way, this line of investigation may open your group up to playing the AoR adventure, Friends Like These, down the road. I think it could easily be adapted to an EoE campaign.

Aren't the PCs in Beyond the Rim working for some sort of corporation? Maybe the corporation is after the same fugitive the lawman is, so he figures it's worth going along with their little mission so long as it means he gets closer to his wanted man. As long as the other players are OK with not being total SOBs (killing innocent NPCs to loot them and other typical murder hobo behavior), you shouldn't have a problem.

More than a couple of westerns have been about childhood friends that went in different directions later in life...or the Smuggler could be a former deputy....or the Marshall could be a former Smuggler..."Just when I thought I was out...they pull me back in!"

This is probably a time to just talk to the two players. Let them know that you are concerned about player harmony, and their characters are going to need to get along. They can have the occasional verbal sparring or playful jab, but they need to work together. If they can't do that then somebody needs to change a concept.

Unless they're both just being doinks I shouldn't think it would be a problem. Paladin and Rogue characters have somehow managed to exist in the same party for as long as their have been these games.

Debt obligation simply means that he owes some money. A smuggler is just a career path not a written in stone "you must do illegal things". Besides, maybe the smuggler specializes in smuggling things past the empire to people in need. Maybe his smuggling is limited to legal things that get around the mega-corporations artificial limits to control prices and keep people under their thumb. Maybe he smuggles out and free's slaves. The same applies to the Marshal. It's just a career description of what they used to do. Maybe their not a marshal anymore. If they are, then consider who the marshal works for. If he works for the empire, then sure he'll have issues with it. If he came from a small frontier world, he'd probably only care about the laws there and not about whether someone had committed a crime on another world unless it was something heinous.

People from disparate back grounds with vastly different priorities work together towards a common goal all the time.

it sure would be interesting if they were siblings...

(just sayin'...)