There is a way of doing that, but unfortunately not yet on baserow.io.
If you were using baserow.io, you can only duplicate tables and databases within the same workspace. There is an issue on the backlog (Move databases/application to another group (#1359) · Issues · Bram Wiepjes / baserow · GitLab) that introduces the functionality to move/transfer a database to another workspace. When this is finished, you can duplicate the database and then move it to the workspace of your customer.
If you’re using the self-hosted version, you can use the structured export/import to move databases between workspaces. The downside is that this is only available using the CLI. You can, for example, export all the databases to a JSON + ZIP file. The JSON file contains the structure of the database, and the ZIP file contains the uploaded user files. This can then be imported in another workspace. You need to be comfortable with the CLI, though:
python src/baserow/manage.py export_workspace_applications FROM_WORKSPACE_ID --indent
python src/baserow/manage.py import_workspace_applications TO_WORKSPACE_ID workspace_FROM_WORKSPACE_ID
There is another issue on the backlog (Offline backups (#90) · Issues · Bram Wiepjes / baserow · GitLab) for making this type of export/import possible via the web-frontend interface. This would basically allow you to make an export of a workspace or database by clicking a button, and import this into another Baserow environment.
Another approach you could take is completely self-hosting Baserow and creating your own template, that your customers can install. This does require some technical knowledge on building and deploying Baserow yourself. More information about creating templates can be found here: Create a template // Baserow.
I hope this answers your question 