Obviously you will want a building inspection done (same as when you buy a house), which ranges in price but shouldn't be more than $2,000.For items you can do before hand I would recommend checking on the zoning and also be certain that you can rent the space for enough money to get your desired returns; this can be done by talking with your potential tenants or even walking into neighboring business and asking how much they pay in rent. 

After visiting the places and the neighborhoods it became clear why (I have no desire to be a slumlord). 

He lost all of his properties mainly because rents plummeted, his houses were also older, and renters shifted in to other vacant properties that were much more updated.Contrasting to that, my highly desirable Brooklyn, NYC properties didn't miss a beat during the crisis.I also wanted to add that another Investor friend of mine bought a SFH Investment in East Germantown, Philly.

Suddenly I had the desire to see if I could buy the house subject to.

As soon as they can 1031 up into more desirable properties that are not headaches then they will do so. 

Max 75% LTV so you could pull some equity out if desired.

The low cap neighborhoods - you know those by the beaches- are the most desireable and low cap neighborhoods. 

A beach house with a bungalow in the back, in a tight market, in a highly desirable area...

The ethical wholesaler makes sure that they can close even if their desired buyer pulls out. 

However, I've also read that if the tenants live with clutter, decorate the house in a less than comely manner or make it seem in any way less desirable, it can negatively impact the appraisal.