How much should a store spend on marketing?

Whatever keeps acquisition cost below a third of lifetime gross profit. Percentage-of-revenue rules are guesses; this one is derived from your own numbers.

Why the answer is what it is

Early on the honest answer is ‘as little as answers the question’, because the point is learning rather than volume. The budget should grow with confidence in the unit economics, never ahead of it.

What this looks like in practice

Paid traffic is rented and gets more expensive every year. Every channel you own — email, notifications, your own audience — gets cheaper as it grows.

Attribution is harder than the dashboards suggest. A customer sees six things and the last one takes the credit.

The cheapest customer is the one you already have, and most budgets are spent as though that were untrue.

Where a mobile app comes into it

Push notifications sit on the owned side of that line, which is the whole commercial argument for an app.