I would ask the reseller to show me the stamp of the bag, even is it is already listed on the product listing. This is to prevent any unhappy surprises once you get home as human mistakes can occur.
You should also check that all protective stickers are intact. However, bear in mind for bags like kellys, the sticker on the front turn lock may not be 100% completely intact as the original buyer will open and check the bag, and then when the bag is brought to the reseller, he/she will open the bag again to check again so that will rub off parts of the sticker on the turn lock. So we need not be unduly bothered by it unless the sticker is totally off which shouldn’t be the case.
I’ve bought brand new bags from resellers which comes with crappy wrapping paper, old dustbags (swapped by original buyer or reseller I don’t know but so cheapskate to do so) and lost ribbons. At the end of the day after the excitement wears off our boxes will get dusty/mouldy, dustbags will get washed and we will lose our ribbons and even receipts but seriously much can be done to improve the ‘bringing home a brand new bag’ experience. You may or may not get a lovely orange paper bag too haha.
I will also be careful of ‘brand new kept unused’ bags which could be sitting in closets for years. You should check/smell for any signs of mould.