There are incubators that pair technical and nontechnical founders, or provide advice to technical founders about marketing etc. You may want to consider someth

There are incubators that pair technical and nontechnical founders, or provide advice to technical founders about marketing etc. You may want to consider something like that, where you can meet and evaluate people in a more structured way. Maybe its unintentional, but the way you described the person you met - serial entrepreneur, online marketing, hustling, makes them sound sketchy. I'd take them out for beers (or whatever today's equivalent is) with a few of your good friends and see what kind of vibe they get. For this kind of thing, I think gut feeling and other people's impression goes a long way.