Someone too lazy to update their listings to reflect a rising sticker price (or not wishing to do so for other reasons) isn’t too good to be true. If they’re an established business selling new-in-box items at more than the wholesale price they would have paid (around 50% of the lowest sticker price the good’s ever been sold at isn’t a bad estimate), then you may have found a genuinely good deal.

It’s when someone starts selling at below their cost (unless it’s obviously to clear out old inventory or the like) that things get suspicious.