John, John, John...where did your mother and I go wrong...?
There are a ton of problems, some more intense than others, depending upon your location. In the mid-Atlantic states, stores like Farm Stores, WaWa and Sheetz are cutting margins to the ribbon, while mounting mammoth C-Stores the average guy (or gal) can't build or support. Then, Sam's Club, Cosco, BJs and even Safeway are coming in as well, further cutting the margins in other areas. That seems to be a bit of a wave of the future. I have literally seen a dozen or more guys I know who have just thrown in the keys and closed the doors on their stations, after I (and other Brokers) told them they had nothing to sell!
Combine that with the Dealers in virtually all Stations only being given three (3) year leases, leases that are enormously costly and wholesale pricing that is (in some states, illegally) districted. Your worst enemy is frequently the Oil Company whose brand you carry.
When Gas prices go up and down like a yo-yo, some Oil Companies are forced (or maybe scheming) to restrict supplies. You can find yourself without Gas, but they don't cut you a break on Rent, during those times.
C-Stores are undoubtedly where you get your money. Go back to my first comments about the competition. Gas largely goes for Rent. But many Oil Companies force you to live with 24-hour operations, even though you may earn a Gross Revenue of $20 during the hours between midnight and 6AM; but you are still paying the help, during those hours. If you have no traffic, even a C-Store does you no good.
I could go on and on, but to sum it up I will tell you, unless you own the property, I would not buy a Gas Station at this point. At least, if you buy the property, you gain equity in the Real Estate over time, and you are not at the mercy of the Oil Companies or Jobbers for your Rent and renewals.
Without the property, at its very best, a Gas Station is not an investment; it is merely buying yourself a job. And frankly, you could earn better money as a waiter in one of your Restaurants, without the risk, the headaches, the pressure...