so, buying online, if it's got 1 dead pixel you can return within 14 days as an unwanted purchase (or at least tell them you're going to return within 14 days), but if it's shop bought and you find a dead pixel then they don't need to refund/replace unless its outside the manufacturer's spec for what's faulty (usually about 5-6 dead pixels, or 1 bright).
Yes this is correct. As for store bought I think that the general MAX allowed dead pixels for shop bought monitors is 2 dead pixels per million pixels (rounded up) (i.e. so for 1080p which is just over 2 million it would be 5 dead pixels, for 4K it would be 16!!), however some manufactures set a more reasonable policy, but I think that 2 per million is EU law (I think).