Like a marriage, you should be in sync with your founder/partner. Anger, evasiveness, defensiveness when planning for the future are all red flags.

In fact I've usually had trouble with founders that were so slick and evasive I didn't notice they were not on the same page until too late. Later I learned they were listening at doors, making comments to team members to divide us, and even in one case following me to a dinner with an old friend (to make sure I wasn't being recruited).

So an obvious non-fit like describe by the OP is maybe an easier situation.