I've done camera work and the plumber said they see light root growth, but I could clean the pipes annually to prevent growth and back ups.

Although 15 years is an eternity for an investor:)Why'd you pay "market price" if it needs work and under-rented?

You can't go off of the cost estimate on permits and even beyond that, design, site work and a number of other factors will play a significant role in costs.

A wise investor will not try to get rich quick with shortcuts.

Great work, and I hope you find continued success!

Do you plan to stay in this area for a while and work and live in the same house?

In addition tenant flips take work and have costs.  

They are going to put in a certain amount of work and their own money on marketing, photos, their overhead costs (agents are independent contractors who pay their own E&O and health insurance, income taxes, MLS dues, NAR dues, continuing ed requirements, etc., etc. all out of their commissions before they get to keep any $), their time, etc. then they also have to split anything they make with their brokerage. $4k would be losing money for me but again it sounds like a lower cost of living area.   

Does it need work and you want to renovate or are you happy with them and maybe want to offer an extension or renewal? 

-Administrative Burden: Managing substantial services may require more administrative work and potentially higher costs in terms of time and resources.Some investors do use creative strategies to maximize tax benefits, but this particular approach of converting long-term rentals into an active business reported on Schedule C while providing substantial services is less common.