Properties are sitting on market for a bit longer now that supply is slowly creeping back up. 50 days isn't too terrible compared to the greater PHX area. 

Now, it’s time to explore the various methods of investing.

I'd send out 500 at a time, using a different mailer/method weekly.

A quick google search of your state indicates the following regaridng timeline to give notice:30 daysFor tenants who have lived in the property for less than one year, or have a lease for less than one year60 daysFor tenants who have lived in the property for more than one year but less than two years, or have a lease for more than one year but less than two years90 daysFor tenants who have lived in the property for more than two years, or have a lease for at least two yearsI'd definitely touch base with an eviction attorney in your state to ensure you are not missing any steps and to have the attorney as a backup option in case the tenant does not vacate easily.

But why would that make them want to use this financing method?

Lots has changed over the years.Managing it yourself from a distance can be done, but it will require your team to be built and for you to have back up strategies if guests need attention and you're unavailable. 

I have heard that it is common practice that private money lenders collect a monthly fee thru various methods, I'm trying to determine what those methods are.   

Unlikely.The backup plan is to have a strong lease.

My experience with friends/some clients is get their numbers via whatever method you can and reach out via the phone.

We have HELOC money available from our primary and one of our rentals at about this same rate, so that could be a backup plan.