An authorized retailer is a store or other outlet that has been specifically authorized by a manufacturer or other brand to sell its products. This authorization may be in the form of an exclusive agreement, meaning that the retailer is the only one allowed to sell the product in question, or it may simply be a non-exclusive arrangement giving the retailer permission to carry and sell the product alongside others who have also been authorized.
The main advantage of buying from an authorized retailer, as opposed to another type of store, is that you can be reasonably sure that you are getting a genuine product. When you buy from an unauthorized retailer, there is always a risk that the product may be counterfeit, especially if it is being sold at significantly below market price. Even if the product turns out to be genuine, there is also a risk that it may not be covered by any warranty or guarantee, meaning you could end up out of pocket if something goes wrong.
Of course, even when buying from an authorized retailer there are no guarantees – sometimes products turn out to be faulty or not quite what you were expecting. However, as long as you keep your receipt and any relevant documentation safe, you should be able to return faulty goods and get a refund or replacement without too much trouble.