It's pretty arbitrary. Even if it's not been declared as a purchase (like second hand books being sent as a gift,) they still charge customs duty. And there's the luck of the draw, sometimes you end up with corrupt post office employees who hold packages until you pay bribes (this is most rampant when in less developed areas where they expect that people are more likely to just suck it up and pay instead of finding someone to complain to.)
I remember during the Incandescent postcard days when B7 sent me an illustration. The post office asked me to pick it up at the local office and charged me 500 pesos (you can usually tell it's tacked on because it's always an exact round number) for storage fees or something...and more recently the comics that Kahlia sent me, where I had to pay around 4-5 thousand pesos in customs charges for a small box with 70 single issues of Superman and a small plush doll.
It used to be that FEDEX and UPS were safe methods of delivery, as the customs charges were settled on the sender's end, but UPS recently changed policies in here and they now settle the customs charges on the recipient's end by default (there is an option to settle customs charges on the sender's end but they have to specifically ask for it, I think.) FEDEX, I don't know. Haven't tried it for years.
