> "The authors concluded, "the next time you need a little-pick-me-up, you might consider interacting with the Starbucks barista...thereby mining this readily available source of happiness"."
Baristas, waiters, etc. are paid to provide services, not necessarily to be conversational partners. From their point of view, their choices are "be nice to this person who is chatting you up" or "upset the customer", so it's not really a stranger interaction, it's a client interaction. They're also likely pretty busy, so keep it short and sweet - i.e. "Thanks, this looks great, have a nice day".
Another issue is class stratification - far and away, this seems to be a delimiter in at least large American cities. Most people won't welcome a homeless person coming up to chat with them; people in business suits are more likely to talk to other people in business suits; etc. This kind of polarization is more of a divider than what corporate media likes to focus on, i.e. race and gender.
Finally, there's the inevitable issue of dealing with the occassional hustler or con artist... see this Atlantic article, 'Stranger Studies: Cities as Interaction Machines' (2010), which concludes with this one-liner:
> "Although I do not recommend it, by the end of the semester my students could likely launch successful careers as grifters."
https://www.theatlantic.com/technology/archive/2010/09/stran...