I agree with all the above..
But I was once pulled up by a coustomer because I charged her ten quid for a 5 litre tin of white vinyl matt emulsion..she said she could have got it in B&Q for 9.99 (yeh I know!!!)
She said she wasnt quibling about the penny difference (hmmm
) but though as I was in the trade I could have got it far cheaper (conveiniently forgetting the fact I saved her a trip to the shops by picking it up!)
I explained to her that the sheds get the paint for peanuts and I cant do anything about what they charge...but the main thing was trade paint is better quality and covered better.
But she came back with the point that if it needed two coats anyway of either paint then whats the difference...fair point IMO.
Quality wise I dont really think theres anything in it, most paint, even the home brand stuff in the sheds will last...its when you start buying un branded bargain bucket stuff your going to run into problems.
The main difference is in the application, opacity and odour..retail paint goes on easy, smells nice and has a jelly consistency..(which misleads people into thinking its thick..it is til you stir it)
In order for retail paint to have these qualities they have to add somthing...in order to add something you have to take something out..the pigment..hence the reason retail paints dont cover as well.
http://www.dulux.co.uk/advice/questions/faq/faq_005.jsp