To mitigate in the future ask for a conditional waiver together with his invoice before you issue a check, and unconditional waiver together with your transmittal receipt with (guarantee that he paid all subs and suppliers) of the check.For him not to put a lien, call his contractor's bond company, let them know that the contractor abandoned the project and you would like to file a complaint and want to know their procedures.

He even talked about having the keys for an abandoned property and able to rent it out.

It gets you on your way.Note that I have not suggested that you abandon any parts of your plan, which is a good one. 

Came across an absentee owner/abandoned 2 bed 1 bath a couple weeks ago.

But if it is obviously abandoned, say so in the letter.

Posting ads that state something like "Need a Buyer for an Abandoned House" or "Investor Special!"

I bought my grandmas house for the taxes that were owed on it total about 2,500 bucks its been abandoned for 9 yrs.

The property was the ugliest house in the neighborhood and was abandoned mid-rehab when the insurance proceeds did not cover the cost of to repair the home after a small a fire.Because I purchased the property in Cash and bought it As-Is the local building officials were not in the loop and immediately put me on their Sh*T list when I filed for permits.

Like ALL of the guru courses you adopt some of the materials for your use and abandon some.

It was in fact very surprising to me to see the same houses that stood abandoned in 2008 still untouched till today, despite such a shortage.