From my observations, most  properties marketed by wholesalers are not  “off market deals”.

A few observations:1.

By observation from a few I've seen in the area:1) Find old guy, hopefully with limited faculties not aware of the market value of his property2) Tell him you love his place and will enjoy owning it and that you're his good buddy who cares about him.3) Offer him at least 10% under FMV and tell him no one else is going to pay that much.   

Any other clues or observations to make to understand if the tenant is good?

If you use any of the major mailhouse services, like Yellow Letter HQ (a service I can personally vouch for), they offer a variety of templates and even provide text suggestions.A smart way to analyze this strategy is by observing people in your local market who use mailers and identifying what works or doesn’t work for them.The simplest and most effective way to test this approach is to pull a hyper-targeted list of distressed homeowners and run a small-budget mailer campaign.Hope this helps!

I don't mean to sound rude or insensitive, it's just my outward observations.  

From my observations most investors are better off going through a more natural progression of growth.

The biggest issue I observe amongst real estate investors is the inability to articulate the reasons why they should transfer properties or simply own properties from day 1 in an LLC.

I found an auction property, drove by it and sent him a long email with my observations and values that I came up with.

This is when most guests will observe any issues, and it can be nipped in the bud right away.