Is MacBook Air item 1308579, model zouu3ll/a new or refurbished, is it reliable?

We are all other users here and do not work for Apple, so we do not know if something is reliable, new, or used. You need to check with the store/seller you want to buy this from. If they give you the serial number, you can enter it here:

https://checkcoverage.apple.com/

All we can say for certain is that if you are purchasing it second hand or from someone other than an authorized Apple retailer, then it is by definition, NOT "new".