I think it is really difficult to charge enough to make it worthwhile. All it takes is one person backing their trailer into your landscaping, running over your pet dog or cat, bringing a guest that behaves inappropriately and gets hurt or messes something up, plus the security issues, plus people bringing their dog and letting it loose to chase your horses or pee on your hay you have stacked in the aisle, leaving manure everywhere, letting their horse paw through footing and dig up the arena base. Plus, people do the darnedest, most dangerous things when left to their own devices–things like let a beginner try out their green broke sale horse, overworking horses or rough riding, crazy style longeing, etc. You 100% need to be there to supervise.
It has been my experience that while boarders are invested in following the rules and treating their home facility with respect to help keep it nice, guests can be much less respectful and much harder on a facility.