It's something I am thinking about. Although we assume many can do it and it's simple. Repairs & servicing is a very busy side of the trade. Shops are crying out for good mechanics.
It's not just punctures, its everything related to bikes that create business daily.
Cables, chain sets, headsets, just taken out of shed service, tyres, tubes, gear adjustments and so on. The classic phrase I hear is
"just purchased this online" can you fit it for me"
I think some people assume bike shops are the only way, the mobile guys I see dont really have good websites or market themselves very well.
There is a company overseas who went on a version of Dragons den with a similar idea. Got invested started out with 1 or 2 vans and now have 34 vans which they franchise to mobile mechanics.