Accredited Installer
Quick answer: An accredited installer is a professional detailing workshop that a coating manufacturer has vetted, trained and signed off to apply their professional-grade chemistry -- and to register the manufacturer-backed warranty against the customer's vehicle.
"Accredited installer" is the customer-facing version of a formal contract between a workshop and a coating brand. Manufacturers who make the strongest professional coatings -- Matrix, Ceramic Pro, GYEON, Fireball and others -- only sell their top-tier formulations to studios they have inspected and certified. That inspection covers premises (clean, lit, climate-controlled), staff training, application protocol and insurance. A non-accredited installer, by contrast, can only access the brand's retail range -- a milder formula with no manufacturer warranty attached.
The term overlaps with Accredited Agent / Accredited Outlet -- manufacturers use different labels (Authorised Installer, Approved Applicator, Certified Detailer) but the underlying arrangement is the same. See the Accredited Agent / Accredited Outlet entry for full detail on what accreditation involves and why it matters for your warranty.