I've only ever had one customer put their own price up.
A quid.
A few years later-she binned me.
She'd had the decorators in and they told her WFP was ruining her painted windows
Ho hum.
Don't you just hate that when crap painters come along and slag wfp off only to find their paint job is off poor standards cause they're too lazy to rub the wood smooth and just paint over the existing stuff which just flakes off after a short while. Always go back and see the ex customer when the paint job deteriorates and comment on how good a job the painter done and then I recommend my friend to come along and put the job right and normally end up getting the job back 
I have a good painter I recommend to my customers as he does a top job and in return of getting him new work he looks after me 
I also read that new paint is not as good as old paint because there isn't any lead in it anymore.
I seem to remember the guarantee only being 5 years on paint but used to be 10. Willing to be corrected by someone with more knowledge though.
It's down to the Bureaucratic mentality of the EU and it's less about the painter.
Every time the EU decrees that paint be re-formulated for reasons of COSHH, the new product is almost always inferior to that which it replaces.
Lead was the first issue - lead based gloss paint when used for exterior work could have a life expectancy of up to 20 years - the current Dulux Weathershield is probably good for 5 ! Most telling is that the current Weathershield Gloss has the same life time in either oil or water based versions, in fact the water based alternative seems better suited to the UK weather. Even high performance coatings will fail in under a year if exposed to excessive sunlight or extremes of temperature - preparation, though vitally important for a good result, is less important than previously as generally the paint system will have failed externally long before it comes unstuck !