He comes across like a very basic con artist slime-ball to me, preying on insecure people by acting confident and successful, which people mistake for actual success.

Flipping can look very appealing but in the beginning be ready to make many mistakes unless you are partnering up with an experience flipper.

The mistake you are making with your conclusion is assuming there is a "good list".There isn't.Many people will promise you that cold calling texting and postcards/mailers is the way to do this, but I challenge you to stand on your own 2 feet and think on your own.

You made the same mistake I did which was to agree to renovate an existing space that someone was living in.

@Marc ShinRecommend exploring as many sources as possible to get referrals AND cross-reference them to get as much accurate information as possible.Check out NARPM.com, BP’s Property Manager Finder (BiggerPockets: The Real Estate Investing Social Network), etc.Also, encourage you to learn from the mistakes of others - by reading posts here on BiggerPockets about owners not having their expectations met by their current Property Management Company.

Cash for keys is a means of erasing a big mistake and rarely works in the landlord's favor.If you understand the law and how to handle tenants, you'll never have to pay them to leave. 

He just said "now I don't feel appreciated, let's settle those favors I did you before we proceed any further" and sent me an invoice for $2K for the lost materials + time with the break-ins.Overall, the job seems to be ~80% complete but with poor quality, and I will absolutely need to hire someone else to fix his mistakes.

I recommend using an experienced agent to help you buy especially off-market deals to help avoid costly mistakes.  

Anyone have an idea of whether this is a mistake in the book or my/Google's calculations?

You made a mistake in the very beginning by unclogging the toilet.