Welcome to the Seller Community @fatcat!

You might find Square’s Customer Directory useful. This free feature allows you to build a profile for each of your clients. You can add a customer to your directory before or after each sale using a form in the Point of Sale app. In this form you can can record your customer’s name, email address, phone number, address, and date of birth if needed. You can also upload an image to a client’s profile. For example, if you wanted to save a sketch for a particular client you could add it to their profile and to have it to hand for their next visit.

You can also use your Directory with other business tools like Email Marketing or with Square Loyalty, which is Square's rewards program.

There's an overview of the features of the Customer Directory here. When you’re ready to get started this Support Center article will show you how to enable customer management from the app and add customer’s information and images as well.

I hope this helps but let me know if you have any other questions!