I find it's generally safe to just have items delivered straight to your main or side, whichever account you want the item to end up on
I've seen people who do create sides/middleman accounts to preserve anonymity, but it's uncommon and not needed in my opinion.
- All NC items sent via gift boxes were, in the spirit of the game, intended to be purely gifts. Neopets itself doesn't endorse "trading values", or even "trades" really, everything is more looked at as an exchange of gifts between two people
- Even on the NCC people genuinely gift each other things ALL the time (there are even huge gifting boards where people post their wishes and receive gifts from kind strangers)
- And when trading legitimately on the NCC, it's very common for people to ask their trader to send items all over the place, be it to a side account, or to the main/side account of another person that they're trading with, or to a friend (and furthermore, people move items between their main and side accounts frequently); which explains why an account would be receiving items and not sending them out in return
^ Reasons why it's kind of hard to definitively distinguish if an NC item that was received was a gift vs. part of a trade vs. bought