So to ensure that .. it’s better to match box serial number with the serial number on the AirPods itself ?
If it's 100% original you will be able to:
1) confirm the serial number with apple website
2) call up apple hotline or go to apple's website and register the warranty yourself with the date that you purchased [exemption to this is that the set is authentic but manufactured more than 3 months ago, so you will encounter error when doing self registration for warranty]
3) check that the packaging is exactly identical with those at Apple Store (stickers and fonts are 100% the same, plastic seal is not those low quality DIY shrink wrap)
4) check that the serial number on the box tallies with the serial number engraved on the AirPods case
5) bring it to apple store and ask the staff to verify authenticity