The interesting question here isn't whether Manchester merchants should hire locally. It's why merchants everywhere else in the UK should consider Manchester.
The city delivers work comparable to London's at 20-35% lower day rates. Since the UK has a single time zone and nearly all Shopify work is remote, the geographic argument for paying the London premium is weak.
For Manchester merchants specifically, local helps in four situations:
Physical work
Product and lifestyle photography, in-person training, retail POS setup, warehouse visits.
Stakeholder-heavy projects
Where in-person discovery workshops on a large build justify getting people in a room.
Fashion and apparel depth
High SKU counts, rapid seasonal turnover, and the returns dynamics that come with clothing.
Speed of assembling a team
Manchester's scene is large enough to source a developer, designer and marketer without going national.
For everything else, search nationally and let rates and category fit decide rather than geography. That works both ways — Manchester merchants shouldn't restrict themselves to Manchester, and merchants elsewhere shouldn't overlook it.