Tenants sometimes damage properties, and depending on local laws, they may be hard to get rid of. You'll be the one they call in the middle of the night if the roof is leaking, and you'll have to clean and perhaps freshen up the property between tenants. You can outsource much of this to a property management company, but it will take a cut of your income, often about 10%.
Equally, you can charge businesses to ‘claim’ their listing, a method used by many large directory sites like Google Business and Yelp. This involves companies paying to upgrade their listing and adding information such as their web address, social media links, images, and more. Other revenue streams include charging for ad space, adding affiliate links and even charging for services and products on your directory site.