EDIT: Oops, didn’t realize this thread is a couple years old.
Maybe this is not relevant at all, but chiming in to say that I’m a US millennial and just learned what “finna” means. I’ve also lived abroad for 6 years and am not a huge social media user. Is it possible in some of the cases you named that the Buyer is not in the age group for a certain type of slang, which would be why they don’t understand it? And is it just that they’re not responding to it, or they ask what it means?