Thanks for posting! When you wrote, "While some rules have specifics for this [interacting], Fortunes Won & Lost and Mission St. Mary do not", which rule-sets were you referring to? Which rules are the most detailed/advanced?
Probably the Talk the Talk style tests found in 5150: Urban Renewal, And a Bottle of Rum Free Ports, Larger Than Life, etc. where you roll Rep # of d6 and compare number of successes. I love this type of opposed challenge, because you can have a variety of results beyond pass/fail.
The way Interactions are presented in Legends of Araby and 5150: Bright Lights Back Alleys (I think that's the title) work differently, but these are interesting in their own right due to the inclusion of possibility rolls within the tables. There are gaming situations where I would prefer this style even more than the Talk the Talk tests, because the subsequent die rolls can branch different ways, making the results even more varied.
Since these tests are included in published product, I don't know how much more detail I should provide.
Regarding gambling, Faro has been provided in And a Bottle of Rum (base rules or Free Port?) and Six Gun Sound. This is a fun mini-game to play.