Well yes you pay the most affordable prices for materials they mined, and you you earn money for selling those materials to others at fuel stations, but your post earlier was saying that the seller would have to pay a fee for selling you items if I read your post earlier, correctly
I'm guessing you're new to this sort of thing so I'll try to break it down.
If you're selling fuel you're probably not also buying it at your station. That's a waste of time if you can simply tax the commerce going through your station and not have to worry about keeping an inventory yourself. The people buying fuel and selling it are exploiting market differentials, not paying miners. If you want to buy fuel you're probably not going to actually pay miners for it at your station. You're going to get in a cargo vessel, fly somewhere where its a lot cheaper, buy it there, and haul it back to your station.
You're also probably not paying other people to mine it directly. That's going to be more expensive than buying fuel they're already selling. There's very little incentive for people to take your money unless you can pay them more than they can earn themselves. If you're buying you're just posing a buy order that says "I buy X amount of rocks at Y price"
If you DO have employees, you're not paying them to mine ore. You're just another customer for however much ore they sell. MMOs work like this because players can't be expected to follow a schedule so the concept of hourly or salaried pay doesn't work. If you want to lead other players in an economy like this you have to ask yourself what you're doing for them. If its simply buying their minerals you're going to have to pay more than someone else would, which means you don't really have room for a profit margin as you'd need to jack up the price even higher to sell it. Anyone willing to pay your markup could just pay your miners directly because you've made yourself a pointless middleman.
For example:
The way we paid our miners in EVE was we'd collect and refine all the ore, use the minerals for manufacturing, sell the manufactured goods for far more than the ore was worth, then pay the miners 110% of market value for ore as well as maintain a fleet of corporate ships with corporate insurance so that if something happened to them they wouldn't be out their own money. They could also submit buy contracts for anything they wanted shipped to the station so they didn't have to go long distances for anything else they wanted like combt ships or ammo or whatever. Their job was only to play the game like normal and get paid better for doing less travelling. They won by getting paid better and not having to hire or do their own shipping, the corp won by having a cheaper source of minerals than buying them on the open market, and I won by being CEO and taking my cut of the profits after expenses. Unless you can create a win for the players under you, you won't have any.
Supporting that business we had a hauler responsible for moving shipments of our goods and buying stuff on their contracts, and as manager I spent most of my time doing logistics to keep us ahead of the curve by figuring out new markets to sell to, managing production, and doing diplomacy and cutting deals with people for discounts or security arrangements in return for using our facilities. I also occasionally hauled the more dangerous shipments myself as I was specced for smuggling from my career before being a CEO and had good smuggling ships and skills.
My business model was selling a kind of high profit ship technology, but the principle applies to fuel (which would have a similar economic profile as ammo does in EVE) as well. If your business is to sell an easy to make thing, you're probably going to need to sell a LOT of it to make money. You're probably not going to sell that much at a fringe gas station. This is why IRL gas stations typically don't mine their own oil and in stead buy refined gasoline from oil companies. Its a win for the oil company (who can sell gas to thousands of distributors) and a win for the gas station (they don't need miners and prospectors, they just need a truck)
Taxes and service fees (for example refining ore) are the typical model station owners use to pay upkeep and make profits in EVE and most other MMOs where they're available because its more profitable and less overhead. If you want to run a gas station, your job isn't mining and making gas, its running a gas station! Everyone needs gas, gas sells itself, your job is, like IRL gas stations, to strategically place your station for the highest amount of traffic the furthest away from competition. You could make it only sell gas you bought or harvested, but if you do so you're leaving money on the table. In an MMO there's no corporate legal team hovering over you demanding that you sign a contract to sell only one brand of gas, and there's no tank that means you can only store one brand of gas. Your location alone can drum up plenty of business as sellers make the trip because they can sell fuel for more, and buyers make the trip because its placed conveniently along their route.