1. Check same model at different stores. are any other stores offering roughly this price ?.
2. Check the reviews , is it legit or from bot?
3. is it verified store?

btw last time during samsung days, ayam always buy like this .so far no issue. they say its unlocked set, cheaper than retail by 300-400, ayam used it just fine . just that the box is opened for warranty purpose or something . but as long as got warranty online then its fine .