When the last shop on an island closes, the loss ripples far beyond the shelves. The parcel collection goes, the noticeboard goes, the person who notices you have not been in for a few days goes. Community-run shops grew out of a refusal to accept that. They are now a familiar part of island life, and they run on rules worth knowing if you live near one.

What makes a shop a community shop

A community shop is owned by the people it serves rather than by a chain or a distant landlord. Most are set up as community benefit societies or co-operatives; some are charities or companies limited by guarantee. Members buy a share — often for a modest one-off sum — and each gets one vote at the annual meeting, whatever they paid in.

That structure shapes everything. Opening hours, stock and staffing are decided by people who have to live with the results, and the shop can be run for something other than profit: keeping a service alive, employing a couple of local people, providing somewhere to sit with a cup of tea on a wet Tuesday in February.

Why island shops face a harder sum

An island shop carries costs a mainland one does not. Freight comes across on a boat, which adds money and risk: a cancelled sailing is a missed delivery, and a missed delivery is a gap on the shelf. Trade can vanish for months in winter and arrive all at once in July. With no other shop for miles, it has to stock things no supermarket would bother with — gas bottles, hardware, bait, a spare pair of wellies for a visitor who packed badly.

Many also carry far more than retail: a post office counter, a cafe, a parcel point, a cash machine, a Wi-Fi hotspot, a warm space in winter, and the informal answer to "is the ferry running?". That is expensive to staff and hard to fund from the margin on milk.

How the money works

Most community shops are funded from a mixture of four sources.

Community shares. Local people, former residents and visitors buy withdrawable shares that carry a vote and usually little or no interest. This is not a savings account. The money is at risk, the shares are not normally transferable, and withdrawals can be restricted. Read the offer document properly, and take independent financial advice if the amount matters to you.

Grants. Charitable trusts, the National Lottery and local authorities often fund capital projects — a new building, a refit, refrigeration, insulation. Support organisations such as the Plunkett Foundation help community-owned businesses with applications. Grants rarely pay the electricity bill.

Loans. Social investors and community finance providers can bridge a gap, but the money has to be repaid out of trading.

Trading. This is the foundation. A community shop still has to sell what people want at prices they will pay, and it has to understand its margins. Goodwill cannot cover an unsustainable cost base for ever, and budgeting, bookkeeping and the choice of legal structure are worth paying a professional for.

Who actually runs the place

A typical shop has a committee of volunteer directors, a part-time paid manager in all but the smallest operations, and a mix of staff and volunteers behind the counter. Directors set strategy and carry legal responsibility, which is why the paperwork matters more than anyone would like: food hygiene, health and safety, safeguarding, data protection, licensing if alcohol is sold, and a written volunteer agreement.

Before joining a committee, ask three questions. How healthy are the reserves? How many hours a month do the current directors really spend? And what happens when the manager is on holiday?

Volunteering: what is genuinely needed

Shops often say they need "more volunteers". What they usually mean is something specific.

• Counter shifts, usually two to four hours, on a rota fixed weeks in advance.
• Cover for holidays, illness and ferry disruption — the hardest gaps to fill.
• Deliveries to people who cannot get in, and to outlying parts of the island.
• Baking, soup and cake for a cafe or a Saturday morning.
• Driving to the terminal for stock, or meeting a delivery off the boat.
• Practical maintenance: shelves, paint, gutters, light bulbs.
• Bookkeeping, payroll and grant applications.
• IT support for card machines, the till system, the website and the newsletter.
• Committee work, including chairing and minute-taking.

And the unfashionable one: company. For some customers, the conversation at the till is the main reason they came in.

How to support your community shop

The most useful support is routine rather than dramatic.

1. Spend there first. Buy the weekly basics from the shop even when the big supermarket trip is cheaper for some items.
2. Become a member. It is usually inexpensive, and it gives you a vote and a reason to read the accounts.
3. Take one regular shift rather than promising to help "whenever needed".
4. Ask what they are short of — a freezer, a van, a laptop, a qualified treasurer, someone to help with the books.
5. Tell them what you would buy if they stocked it, then buy it when they do.
6. Turn up to the annual meeting. Complaints aired in the queue are less useful than questions asked in the room where decisions are made.