Newbie pack items are meant to be "non-tradeable" meaning that you can never sell them to get the NP unfortunately

They are there to introduce you to the different kinds of items on the site... for example, your Starter Paint Brushes are an "intro-version" of real paintbrushes (that are often much more expensive) - these paint brushes are used to change the color of your pet. Liobits and Weeble are two petpet items, which can be attached as a companion to your pet.

I think one reason they aren't sellable is that if they were, some people might create tons and tons of empty accounts, just to get their newbie packs and sell them for NP.

There is no way to sell items bought with NC. They will stay on your account forever

Lastly, there is an important different between an item's Estimated Value (this is what shows up in the item pop-up box) and an item's real value (this is the number on shop wizard). The Estimated Value is only a guesstimate -- what the Neopets item system considers it to be worth, and what it will be sold at in the official Neopian shops.

However, once an item hits the "real" economy among users, supply and demand takes place and can turn a 1,000-estimated NP and make it worth 3 or 4 np (like your Blue Ixi Plushie), or it can take a 5,000-estimated item and make it worth 200,000! Always use the Shop Wizard price when buying or selling

I hope that helps! Feel free to respond if you have any other questions =)