When a web visitor is known (cookied), Marketo forms will pre-fill fields with their information by default. If you want to turn this off, here’s how to do it.
Form Pre-fill is enabled by default. Landing page level pre-fill settings and admin level pre-fill settings trump the form level setting:
Form > Landing Page > Admin
Go to Marketing Activities.
Select your form and click Edit Form.
Form Pre-fill does not work when embedding a form on your own pages. It only works on Marketo landing pages.
Select one of the fields and set Form Pre-fill to Disabled.
You can also disable form pre-fill at the landing page level or at the admin level.
Click Approve and Close.
When you mark a field as sensitive, preventing its values from being pre-filled in forms, you will see this on the Pre-fill option.