I never had an occasion when they didn't respond after I posted on their door. 

You can still put them on notice saying that it has been noted on several occasions that this person is there which seems to indicate they have been staying in the property in a resident-like manner.

I have also asked on several occasions to get an updated completion timeframe and final (hard) budget number and the contractor is failing to do so.

The broader point being that on occasion things can go sideways – very sideways, and you have to have a deal that can absorb something like that to ultimately come out ahead financially.  

The letter would say that if they are interested they have x days to respond and we will then view the apartments that accepted before making our choice.Our market is distressed and allows on occasion for low ball cash offers.Am I right approaching it in this way?

On the rare occasion you do find one who is qualified it's because they need a temporary place to stay while they look for a house to buy.The other business logic to it is that I get a tenant for a long time, and less vacancy costs.

This can be tedious, but will on occasion produce a path to acquisition that is unavailable to remote buyers, and too much work for local ones. 

Cash for keys has worked for me on more than one occasion especially if they are looking for a new place to live.

A HELOC allows homeowners to borrow or draw money on multiple occasions usually over a period of 5-10 years, as the need arises, up to a maximum amount.* As mentioned above, a home equity loan usually has a fixed mortgage rate, while a HELOC normally has variable interest rates linked to Bank Prime.Typically, during the first 5-10 years, borrowers need to pay back only the interest on the sum(s) they have borrowed.

He brought the deal to me on this occasion, before this he was just inspecting and giving quotes on properties I was analyzing.