Will simply searching using the “Sale Type” feature set to REO be enough or do some agents not adjust sale type correctly?

With a park owned rental, the tenant can simply leave anytime they want and there is no vested interest in them staying. 

Or you could simply knock on the neighbor's door and try to explain your position.

I'd be a bit careful about putting too much stock in negative feedback from tenants as sometimes tenants provide negative feedback on landlords who are simply enforcing the rules. 

Most people simply ask me a question which I guess is easier to ask someone else a question then it is to answer a question :-)The intent of this question was to see what others are doing that hire help in their business and whether they feel like they are getting a good return on their investment.

Simply looking for some guidance on what I should be thinking about in analyzing this type of deal and what considerations I should astutely include in any marketing materials IF i were to tackle this project.

I share this to encourage you not to pass up a deal if it is a good one, simply because it has been sitting longer than average.Go out there and get it!

or he can get approval from seller to do some sampling to see if the tank has impacted the soil. if not, that should assuage most lenders and he could simply fill the tank with sand unless it is regulated....

If the letter is being returned, could that mean the property is simply abandoned?   

I would recommend simply networking as much as you can, attend local investor meetups and leverage your knowledge as an investor to better serve investors as an agent.