I think it's less to do with WFP or trad, but more to do with the individual's work ethic.
One guy will give of his best to ensure he's doing a good job, and another guy will think "oh they will do"
One guy may think that he wants to give good value for his price, and another will think "what do they want for £3.50".
It may take a shoddy worker 3 times longer to build his round, but eventually he ends up with a round full of non complaining customers. I have first hand experience of just such a guy, and I don't think he ever bought a scrim.