We had another rental property performing very well, but ended up selling after we had to deal with bad tenants and lots of damage.

If you are obtaining bank financing, the bank will more than likely want an environmental study performed, these studies can cost $1000's of dollars depending on what is discovered on the property.Is there a need for this type of property in the community?

I've seen and written buyouts where the preferred lenders can exercise an option to cash their stake after 90 or 180 days to get out of the property. 

Here is a high level breakdown of two of the risks that you are carrying1) Liquidity - you are only as liquid as the reserves that you are carrying (which includes whatever is left in your heloc) so make sure that you have enough to cover unforeseen scenarios, personal and business2) Business Risk - as an owner of real estate some of the main risks that you carry are vacancies or non-paying tenants, lower than expected rents (negative cashflow), unforeseen expenses (repairs and maintenance)I would argue that both of these are higher when you are operating at a smaller scale e.g. if you had a fire at your triplex then 60% of your portfolio would be non-performing.

Thus they don't exercise the option and leave the property and the owner finds another "rent to own" tenant and repeats the process.

Most of the time, this is the usual 6%-ish sort of earned commission ("success" or "earned" means they actually performed on the terms of their listing contract and actually brought a buyer for full commission, either through their own efforts, or through the efforts of a co-op/buyer's agent who earns up to 1/2 the full commission). 

Paid Cash and performed a cash out refi.

If they are fine with the estimated net amount of proceeds (much like having a conversation about closing cost credits), you don't have anything to worry about.However if they want a buyer at $X because they want a fast sale, and you agree to buy it for that amount under contract and agree to close fast, you should be able to perform - be it yourself or via someone you assign to.

Are there certain metrics/performance you hold them accountable for (vacancy/turnover)?

A small referral fee is not worth the amount of work you would have to perform to properly analyze every investor, every flip, and every flipper...not even close.