Please don't take this as a jab at you as it certainly isn't intended to be.
That said, you express a really transactional view of human interactions. That seems to be a sad way to view the rest of your fellow humans.
Transactional interactions are a normal part of life but, at least for me, I will interact with people, including strangers, because I like interacting with people, not because I want something from them.
Obviously, when transacting with a cashier, a shopkeeper, a waiter, etc. it's transactional.
But in other circumstances, and even sometimes in those circumstances (if that's not inconveniencing them) I will engage others without any expectations or intent to manipulate or use those folks.
Sure, there are folks out there who will engage with you because they want something from you. In my experience, however (and I've lived most of my life in NYC and travelled quite a bit around the US and less around the world) most people are decent, kind people who aren't out to get something from you or trying to scam you.