Do not store name/phone

My website uses Single Sign On functionality. Users at car dealerships click a link in their dealership portal and are automatically verified/signed to my website using encrypted data. It all works great. However, each person at a particular dealership will use the same dealer number. When they check out, the name/phone/email of the last person using that dealer number shows up. How can I not have those three bits automatically show up upon checkout? I need those fields to always be blank. Address and dealer number are always constant of course.

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