Vetting potential partners

[Dominika M]

Hi, how do you check out potential REI partners? There's a starter article on BP
http://www.biggerpockets.com/renewsblog/2009/9/23/how-to-choose-real-estate-partners-and-the-criteria-to-use
which focuses more on whether the partner is professional.
I'm interested in further details, especially in vetting from afar. For example, i may want to check out 5 people I see on BP before I go ahead and approach one.
HOw do you do a background check? Criminal?
If they have properties online, how do you check if they really own them? Ask for papers or is there another quick way?
There's a lot of partnering here on BP, so feel free to make this a full on guide. All us newbies are wondering.
Thanks,
Dominika