Depends,if it is for sale or the previous owner sold the gas station,there would be a notification on the circle describing that it is for sold.If you are to curious to own a gas station,you may approach the specific GS owner and you can discuss a rate.There are pre-setted value for businesses depending on what is the advantages [Maximum:150000].However,if the GS has been bought buy a specific player then you should do as I mentioned above.Contact him in game and talk for a high demand which gives him advantages.