How do you go about pre-screening potential buyers/rehabbers/investors for your wholesale deals?

Sometimes it is just not feasible to go to my properties. I have a lock box on them, but some people just don't give me the right feeling when they call.

Some questions I ask are 'how soon can you close?', 'how will you be funding?', 'do you have other rental properties, if so how many/where?', etc.

A company I used to work for had rental homes all over the area. It was not feasible to go to the property every time a potential tenant wanted to view it. So we would screen over the phone, and then ask them to text us a picture of their ID, and then we would send the lock box code. 

I've tried this with some buyers, but there has been resistance. 

Does anyone have some better suggestions / questions to screen buyers? Stealing of copper is very common and I am trying to avoid this.