Good business ideas to synergize with rental portfolio

[Allen L.]

What are business ideas that people implement that complement a large rental portfolio? I'm not nearly there yet but I think it's good to plan ahead.

For example, some people start their own in house property management business to take care of their properties and take on others.

Other people become realtors and can deduct their commission with rental property paper losses

While some others have flipping businesses and also use losses from rental properties to reduce taxes from flipping business