Shops cannot exist to only service products and handle warranties on items they never sold.
Disagree - they absolutely can. Why? because it's a service for which people are willing to pay. how many shops we'd have is another question ...
what you say can't exist is all around us with many other sectors ...
car mechanics anyone?
You know of lots of Auto shops that don't sell parts AND
Even for things like transmission / brakes / oil changes they are providing parts and labor. especially on non warranty things.
Even if that were not the case (and it is...) do you know many Auto shops that will let you bring in your own brake pads and rotors and will charge you $20 for the complete overhaul using your parts?
Or replace a car's transmission (if you can find the replacement transmission on ebay...) for $45 bucks?
Changing a tire (when you don't buy the tire from the shop) cost you $5 at what auto mechanic??
The dollars and volume involved in repair only are not enough to sustain a cycling business like they are for other industries...
Even in places like Holland and Asia where the pressures and volume are extremely viable and more main stream, service and supply is the norm.
In asia even the "mobile tire" guys that are in that culture carry parts and equipement and are not service only. Yet they are only trying to run a one man virtually no overhead opperation...