How to delete a supplier or customer?

To delete a customer head to Contacts>Customers and click on the customer name and then click on the edit contact button. You should then be able to use the delete button:

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If the customer was added to an invoice (including any voided invoices) you will not be able to delete it (due to the audit trail). There are three alternatives to deal with this though -

1 Archive the customer. Head to Contacts > Customers and click on the customer name and then hit the Archive button. Archived customers will no longer appear in any drop down lists in the system, however, they will still appear in the Contacts > Customers menu.

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2 Merge the customer into another. To do this head to Contacts > Customers and click on the Merge contacts button. Select the customer you want to get rid of in the Merge This Contact drop-down list and any other customer in the Into This Contact drop-down list.

http://www.clearbooks.co.uk/support/guides/customers-sales/how-to-merge-a-customer/

3 Re-name the customer. Click on the customer name and hit the edit contact button - update the name and save.