I have a few postcards left from other countries, mostly where I lived. I recently started sending them because they are pretty art, animals or landscapes. None of them are famous monuments or other country-specific images. I send them to people who seem to me like they could enjoy pretty postcards in general, not just from my country. I have only had positive reactions so far!
I also have two flag cards, which I am significantly more anxious to send. But if I see a profile of someone who collects them, I would send them one and hope they won’t be mad about receiving a rare country instead of a common one 
And as I was writing this, I realized I have a Disney card travelling to the USA
What a fail. I chose it based on the subject in the picture so I hope the receiver won’t mind 