If you have an Odoo Enterprise version, creating a user for each customer user can indeed increase your licensing costs. However, there are several options available to allow you to create customer users without incurring additional enterprise fees:

Public Signup: You can enable the Public Signup feature in Odoo, which allows customers to sign up for an account on your Odoo website. This feature is available in both the Community and Enterprise editions of Odoo. However, it may not be suitable for all businesses as you may want to restrict access to certain areas of the website or provide customized features to different customer groups.

Use the Portal User feature: Odoo Enterprise offers a Portal User feature that allows you to create customer users without incurring additional fees. This feature allows customers to access a limited set of features in the Odoo system, such as viewing their orders, invoices, and support tickets. Portal Users do not have access to the full range of Odoo features and functions that regular users have, which helps to keep your licensing costs down.

Use a third-party authentication system: You can use a third-party authentication system, such as OAuth or LDAP, to manage customer user authentication. This allows customers to log in to your Odoo system using their existing credentials from another system, such as Google, Facebook, or Microsoft. This approach can be cost-effective as it does not require you to create additional users in Odoo.

Use a Single Sign-On (SSO) system: You can use a Single Sign-On (SSO) system to manage customer user authentication. This allows customers to log in to your Odoo system using their existing credentials from another system, such as Active Directory or Okta. This approach can be cost-effective as it does not require you to create additional users in Odoo.

By using one or more of these approaches, you can create customer users without incurring additional enterprise fees. You should evaluate which option is best for your business based on your specific needs and requirements.