While that may sometimes (most?) be true, it's definitely not always the case. I've had some incredibly kind people along the way offer to help me out in ways that would certainly equal a scam based on this equation, including a few similar to what the OP describes. I'd also like to point out this wasn't a 'random' request, although unsolicited. The OP had business with UA, and was traveling through MEX, so hardly random.

My advice is to just set up a privacy.com account, create burner cards when unsure (with the appropriate limit!), and lower the walls a tad.