Underwriting deals for my clients is half the fun.

Please forgive the question I know it's probably pretty basic but this is just our 2nd deal so we are still learning.  

For your first deal I would suggest a cosmetic rehab to mitigate your risk.

My experience is the listing agent talks them into these deals wanting paid twice. 

For small MFH/SFH you have to find the deal, inspect, estimates and decide what to do, make a deal, get financing, get contractors, manage contractors, pay contractors, then turn it over to a property manager.

And while seller financing is a very common practice in business acquisition, the good deals are not being done with high levels of it.Particularly with smaller deals, and especially with a business like a laundromat, there are cash buyers out there.

What made you interested in investing in this type of deal?

There is a possibility that the first deal you make doesn't go well.

@Doug Henderson  I have experienced business partners in SC like you that are doing solid deals in the Upstate region. 

All rules of thumb are high level down and dirty approximations to be used for quick evaluation of potential deals.