I would say not doing inspections often enough and small problems turning in to expensive problems.I do all my own property management (its is about have systems in place and automating as much as possible)When I do have a vacancy, I turn it around in less than a week, sometimes only a day or so.I tend to have tenants that stay a long time.

I have most of the systems tracked and documented.

I have been investing out of state for over 12 years now and your rate of return is definitely good IF you have the right systems and teams in place. 

Does anyone like one specific screening website or methodology for weeding out good residents versus so-so ones?

You need to assume summer vacancy with no income.You need to have latest fire protection system and carry ample liability insurance. 

What this will allow you to do is get actual bids for the work to be completed and, if necessary, walk away or more likely lower your offer where you can present bids for completing work, versus just guessing.As for the REO stigma, the last I saw for metrics, it was around 20% but the discount is market specific.Best of luck

I just bought and returned a RE system from a guru and I did obtain some useful info.

What about HVAC systems, water heater, roof, siding, electric, windows, etc.? 

System and follow up system if you’re going to market direct to sellers.

I think requiring to use an online system like Venmo and such could be added to your lease for the future so it will be easier for you to keep track of payments!