My journey started out like this. I met someone 8 years ago who was renting on a farm and he happened to have a couple of break barrels. I put in hours and hours of target shooting on the property and before long we were shooting starlings on the farm with the blessing of the land owner. Then one thing lead to another, the farmer told the neighbouring dairy farm about us and that was how the door was opened. I visited the farm regularly and made sure I was only taking shots that were safe and within my capability. As I began to acquire better and more expensive airguns and with endless hours of practicing and tons of lead flying downrange, I pushed my range further and further with consistent accuracy out to 100 yards. If you can hit the target safely and consistently, then you are not ready to shoot at someone's property.
I often text the farmer before coming over as a courtesy and if the farm was too busy that morning, I would not stay and shoot. Over the years I have gained the trust from the farmer(s), showing my capability and responsibility; now I don't need to give them the heads up anymore. They just told me to come and blast those starlings as often as I like.
So thru word of mouth, I now have 6 locations to shoot. This is becoming a bit more difficult as I have limited time with my weekends and I can only visit farms that are in need of pest control. But at least I have options to go shoot starlings, rats or coyotes.
All these are done "free of charge" as like others said, it is a privilege to be able to shoot airguns at someone's property. So the idea of charging for your "service" is really not the right way to go about this. Beside once money got exchanged, there is both risks and expectation that come with it. It wouldn't be fun anymore.