So, I posted the start of a story in the short story crime and thriller forum, "Bar Business." The main character, George is a hitman by "night" and a business owner by day. I want George to have a legitimate business to run so that he has something to do with his time and I also want something where there are a large number of people coming and going. I envision that he will either own outright or have a controlling interest in the following businesses. 1. a pub/restaurant. the meeting place. He doesn't work there, just eats and drinks and takes meetings. This could be attached to #2 and #3 I guess. 2. a hotel/motel. He could conceivably provide rooms to prostitutes to turn tricks in and offer them protection plus enjoy blackmailing opportunities against the customers. 3. I would like the hotel/motel to have an attached garage/gas bar. I am thinking ahead that if he ever uses car bombs or something similar he would have developed some skill in sabotaging vehicles and planting explosives. He doesn't have to start out with all of this. He can buy a partial interest in something, he can win it gambling or he could charm or blackmail the owner of a business into giving it to him. Does this seem plausible to people? There are no tricks to any of it, no secret passages between the businesses for example although that's not a bad idea..... I am envisioning that this setting would work any time period from 1950 to the present.
Is he an independent hit man, or does he work for the mob? That makes a huge difference in how he goes about it. If I were a mobster who needed to get rid of someone, I'd hire someone else to carry out the hit, and that someone wouldn't have much wealth or power and would be eager to please and move up in the organization. (This is why I get Woodstock to do all my dirty work. ) So in that scenario, he probably wouldn't be a business owner, or if he was it would be a very low-profile, low money, mom and pops business. I'd be more inclined to have him fronting as a delivery man of some sort, or maybe a heating and cooling repair man to gain access. The mob boss who hires him could own any kind of business you want. One way your scenario could work as an indie, though, is if your hitman is the owner of a failing business and is desperate. Or has a sick wife or child and needs money. Or, if you want to make it a mob scenario, maybe the mob muscles in and forces him to cooperate, but he decides he likes the game.
In terms of what is fun not necessarily realistic: I like the idea of depicting the front as also a place of doing polite and coded business in broad daylight. Think Gus Fring and his fried chicken joint from Breaking Bad or The Continental from John Wick. There's a lot of stuff in John Wick actually. A call center for placing the hits, a body cleanup service that looks like any normal cleaners. Car shops. Bonus points for being able to use the business to peddle stolen goods. Wasn't there a laser tag shop in Breaking Bad too? And a car wash. And a bug bomb business. Think about all the anonymous storefronts that no one ever pays attention to. Title pawns, payday loans, tax advice.
You could go the ex military route. Say a retired sniper, who misses the action and the thrill of the hunt, and subcontracts out in private from his day job. Figure you could make him a private contract killer, that way he can work for whoever is willing to pay. Just an idea.
Just my thoughts- "Don't get high off your own supply." I don't think a hitman would/should operate any business in any way, shape, or form associated with his night job, especially one that would draw in any possible legal attention at all. One simple health code violation could uncover the truth. Now, if the guy/girl has stake in an RV dealership and maybe runs a used video game store in BFE, that gives the hitman a legitimate income to show on his/her taxes. Hitmen were hired from a fixer in the back of a shady bar and almost never directly from the actual client. Nowadays, you have to go into certain parts of the internet I won't talk about on here to get in contact with one. Even then, you'll never know anything about their identity, and good luck finding a trustworthy escrow service.
I've heard of stories where the mob is in control of restaurants as a front, in John Wick the hitman world uses a hotel chain as a front. A hitman is probably a little more classy so probably not a pub.
If anytime 1950-now works, traveling salesman is a decent bet. Low overhead, easy to falsify or launder money. It could also lead to some interesting points where the hitman scopes out peoples houses under the guise of selling encyclopedias or some such. If I remember right, Al Capone was a "Used Furniture Salesman".