How can I estimate demand in a rental market?

[John Thomson]

I need some advice on testing demand in a rental market before I make an investment in rehabilitating my family's rental properties. I have heard people say they placed ads for their potential rental to see how much interest they could generate. How does that work? How do you respond to inquiries? What other ways could I use to gauge demand? A local agent told me that most landlords in the area don't use property managers, so information is hard to come by.

This is the background: We own 7 rental properties in rural South Georgia: 4 small houses and 2 trailer pads. Our mother inherited the properties from her mother and put them into an LLC to pass on to my 4 siblings and me. Our mother has been the manager of the LLC and of the rental properties. She is closing in on 93 and finally admitted she needed help and was willing to make me her co-manager. I went down yesterday to assess the situation. Four properties have been rented well below what I believe is fair market rent. I knew it would be bad but holy crap! Three of the houses are empty. One is being repaired due to storm damage and needs some additional rehab. The other two need more extensive rehab but could be put in rentable condition. The trailers are not ours, just the pads. But, I'm going to have to evict two of the trailer tenants and I am pretty sure they will abandon the trailers. So, I potentially have two more rehab candidates. I can work out the potential return based on expected market rent but need some feel for housing demand for the type of rental property we have.