Don't forget if he is a self employed plumber, he has to cover all the costs of his business, transportation, tools, tax, insurance, membership to professional bodies etc... He will also have to budget for times when he has little work, as he will not have a steady stream of income like employed people.
What he aid basically.
The plumber also likely has to allow at least an hour for the job so that if it does take longer than expected he has time free (rather than booking solid based on minimum time).
Any tradesman who does call outs will tend to charge a minimum fee, be it via callout charge including X minutes, or an hourly rate (often with a high first hour) even if it only takes 10 minutes.
It's one of the reasons my dad bought all the plumbing tools himself


