REI is more about relationships than anything else.  

Also, agree 100% with @Bjorn Ahlblad renting to family/friends can be fraught with issues and ruin relationships on top of it.  

I know I had a pre-existing relationship with these folks, however, the important underlying lesson is that forming and maintaining trustworthy relationships is extremely important.

This is where the relationship part of the process comes in to play. 

What I will say for lead generation is that these very much come down to building relationships as these folk in my experience don't respond super well to direct mail or cold calls. 

I'll comp their first few deals and give my feedback and my number (Or if I can buy it then I'll just put it under contract) and see how the relationship develops from there.

Agent/Property Managers don't walk away from the closing table and wave goodbye; we enter a relationship with that house and a longterm relationship with the owner.  

Hi, I'm an agent and investor in Westchester I've worked with Doug Smith with Prilolet Law in White Plains on a few deals and have been extremely happy with his willingness to communicate, work together, authenticity and fees. 

It pays to be consistent, stick to your word, and establish strong, honest relationships.

Another notable part of this is buyer has a great relationship with the local bank.