No one said there was a difference in the paint sold. Certainly I have seen Dulux Trade paint in the large B&Q trade part of the store.
Travis Perkins sell the basic Trade paints in all colours. But if you go to a Dulux Trade Centre the product availability , professional painting tools are light years ahead of the diy stores. If the tin says Trade than it is and must be Trade paint.
The answer is that a professional painter and decorator will always prefer to use Dulux Trade paint because it is a superior product that will last a long time, not discolour, nor rub off. He/ she will also have a trade account and obviously get a trade discount as he she is buying considerable volumes. They do not want any customer complaints!
The proof is in the pudding .
This will explain a lot about the quality. I need to check a tin but certainly Dulux will confirm their Trade paint opacity is second to none.