Not all motherboard boxes have seal. I've ordered from Amazon and they didn't. Also some which I bought via direct sellers also didn't. I confirmed this with the official retailers. The content was intact though.
What model was yours?
Off topic, perhaps the Mods can move these to a Flopkart woes thread.
Are you implying some are open box ?
I have not seen any as such but the only reason for which they may do that is to allow for Bios updates. Most have a plastic shrink wrap or OEM seal tape. I would consider anything other than those a red flag and if it's a open box delivery, I will go ahead and check everything.
In this case it was just a small normal tape which was coming apart. The box was also battered. Then the condition of the IO shield confirmed my suspicions that it was indeed used and then returned. Typically they are in a plastic packet; here it was just lying beside the board, and had the wear and tear of when someone had it fixed in the case. It was an ASRock Intel board with a Z790 chipset.