Below is some high level info. on how they work.  

Spencer Hsu I offer full real estate services in Indianapolis and believe I can assist you with your first duplex depending what your price point is.

Initially I was getting my leads this way, however I moved on to use paid services because it was much easier to filter and sort through lots of data.

I have a background in wastewater treatment, I also have some experience in multi level business. 

So obviously the current owner of the front lot property with the nice ranch house on it is less than happy about my road easement thru his front yard and going so close to his house, but he bought his property with full knowledge of it it, and the easement was completed  long before with the services of a lawyer, a surveyor, and it was all properly recorded with the county.  

It also allows you to calculate to the dime your debt service costs based on your estimated hold time.Building buyers lists as a wholesaler is also portent but keep in mind bigger dies not mean better.

And then of course your debt service if you really want to figure positive monthly cash flow.does it work out on paper?

In addition to cash in cash returns and capital gains at sale, I also look at the debt coverage ratio to see if the property can support its debt service in these scenarios.  

Cost will be what @Marc W. said and this is based on level of finishes you want as well. 

My goal is to pay a fair price for good service and not be taken advantage of.