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"tradesman with tools in a van"
Is only broadly plausible as the likes of Toolstation/Screwfix/ your good local builders' merchant has on-shelf of 'everything', (within reason).
Bike mechanic in van has increasingly fewer stockists to call on. Out here in outer north west London the only new stockist of bike components is the nearly year old Decathlon in the Intu shopping centre, (with chargeable parking). Fine for those wanting replacement HG 7/8/9 speed cassettes, but nothing better on the shelf.
I think the future for bike mechanics has to be the self-employed "tradesman with tools in a van" model like for every other thing in your house or garden you pay people to get fixed.
Bring my bike to you? Fuck off it's not a car.