The domain is registered in your business name, in an account you can log into
Whoever holds the domain decides where your website and your email go. Getting one back from somebody who will not answer is slow and does not always work.
How to check: Log in where you pay the renewal. If you have never logged in, or the renewal invoice goes to someone else, this one is not yours yet.
The renewal is on your card, with your email as the recovery address
A domain renewed on somebody else's card lapses the day that card or that relationship ends, and a lapsed domain can be registered by anyone.
How to check: Open the domain account and look at the payment card and the contact email. Both should be yours.
You can log in where your DNS records are kept
DNS is the switchboard for your website and your email. Changing either one means changing a record here.
How to check: Ask whoever built the site where the DNS is managed, then log in and make sure you see the records.
The hosting account is in your name and billed to you
If the site is hosted in a builder's account, it lives or dies with that account.
How to check: Find the invoice for hosting. If you do not receive one, someone else is paying for it, and owns the account.
You have your own owner level login to the website
A shared password or a login with limited rights means you cannot add people, remove them or move the site without asking.
How to check: Log in with your own email address and confirm your role says owner or administrator.
You can get a full copy of the site without asking anybody
A copy you can download is what lets any other developer pick the site up tomorrow.
How to check: Look for an export or download option, or ask where the code is stored and whether you can log into that account.
You are the top administrator of your business email
Whoever administers your email can read it, reset passwords and lock you out.
How to check: In Google Workspace or Microsoft 365, open the admin settings. Your account should be the super admin or global administrator.
You are the primary owner of your Google Business Profile
The profile is often where a local customer finds your phone number. A manager can be removed; an owner cannot be removed by a manager.
How to check: Open the profile, go to people and access, and check your role says primary owner.
You own your analytics and Search Console accounts
Years of history about your visitors stay with whoever owns the account, and cannot be moved afterwards.
How to check: Open each one and check your role is owner or administrator, not viewer.
Your social accounts were created in your business name, with you as an admin
A page created on somebody's personal account belongs to that person.
How to check: Open the page settings and look at who the admins are. You should be one of them in your own name.
Every service the site depends on is billed to you
Forms, booking tools, plugins and themes that are paid on a builder's card stop working when they stop paying.
How to check: List what the site uses (forms, booking, plugins) and find the invoice for each one.
Something in writing says you own the design and content
Without it, who owns the work can be argued about, usually at the worst possible moment.
How to check: Find the agreement or the invoice terms from the build. Look for a sentence about who owns the work once it is paid for.
Tick each one you have checked and know is yours.