Diagnosis is where the hours go, and a clear report cuts it down. Send this before you ask for a quote:
- What happens, and what should happen instead. "Add to cart spins and nothing is added" beats "cart broken".
- Steps to reproduce, starting from a specific URL.
- Device, browser, and whether you were logged in to a customer account.
- When it started, as precisely as you can.
- What changed around then: a theme update, a new or updated app, a new tracking tag, a discount or market setting.
- A screen recording, plus a screenshot of any error message.
The last three items solve more bugs than anything else. An app installed the day before a bug appeared is the first suspect, and a recording shows the developer what "broken" means on your store.
Give access without giving away the store. Never share your store owner password. Developers send a collaborator request from their Shopify developer account using a request code you give them, and you approve it with only the permissions the job needs, such as themes for a layout bug. Collaborator accounts don't use up your staff seats, and you can remove access the moment the job is done.
Keep the live theme untouched. Ask the developer to duplicate your live theme, fix the copy and send you a preview link. You check it, then publish. If anything goes wrong afterwards, the previous theme is still in your theme library, ready to republish.