Go to Tools, then Erase Personal Data in your WordPress admin, enter the customer’s email address and send the request. WordPress asks PaintClarity for everything it holds on that address and clears it.
What it removes: their name, address, phone number and email from their customer record and from every job, the typed signature and IP address from any quote they accepted online, the reason they gave if they declined one, and the log of emails you sent them. Any quote or invoice link you had already sent them stops working.
What it keeps, on purpose: the quotes, invoices and payments themselves, with their amounts and dates intact and the personal details stripped out. You are required to keep your financial records for several years, and data protection law allows you to keep them for that reason. Answering a deletion request should not cost you your books.
Two things are left for you to judge, and the results screen tells you how many of each. Job photos, because they are your own record of the work and can show the property. And any scope or internal notes on their jobs, because free text can name someone anywhere inside it and no automatic pass can tell.
To see what you hold before you decide anything, run Tools, then Export Personal Data on the same email address first.
If you want a customer and all their history genuinely gone, a test entry or a duplicate for example, that is a different tool. See “How do I delete a customer?”