Most monitor manufacturers do not class dead pixels as a fault – unless there is a lot of them (or a cluster close together). This is because manufacturers comply to the ISO standard 13406-2 which relates to the acceptable number of dead pixels based on screen size and resolution.
Information on this can be found through any major search engine typing “ISO 13406-2” and the monitor brand name. Products with dead pixels of equal to or less than those defined within the ISO 13406-2 standard will not be accepted as faulty.
You are however still eligible to return the monitor as unwanted within the first 14 days if you’re not happy with the product.