That's odd because if it's marked as a gift how would you know what was in it!? Or even that it was coming to you?
I'm not sure the best way to handle that situation but from what I've been told it's not usually marked as a gift. I read your other posts and you say that the first package had issues also and was returned to sender. Have you spoken with the sender since the reship and this sencond issue?
Being marked as "gift" or "sample" doesn't make it anonymous, people don't send random packages to random people. It's just used as a means to avoid customs (doesn't make a difference here anyway).
They are asking for a believable declaration of value, a personal statement of what I paid. They know the shipping was at least 70 bucks so it's not like I can say 1 dollar. It's not unusal, they asked me in the past for foreign purchases like chinese cellphones (which usually come with understated values as well in the package).
And the first package was sent back after two weeks because for some reason UPS didn't contact me for this declaration of purchase. They did this time.