Legal boundaries? Seeking private funding for tax lien properties

[Alfred Green]

I found 2 different Craigslist ads recently proposing 20%-36% ROI, which are obviously tax lien properties in various states.

I've considered seeking private investors to fund this while making a small percentage off this myself. The main question I have is this:

Is this legal?

I'm aware of the SEC protecting people scamming them, but I am not aware of the actual boundaries. Can this be done? I'd like to know if this is something worth pursuing--or if it's illegal.