After a complainant makes a prima facie case by asserting that a product or service is not accessible, the manufacturer or service provider to whom the informal complaint is directed bears the burden of proving that the product or service is accessible or, if not accessible, that accessibility is not achievable under this part or readily achievable under parts
6 and
7. To carry its burden of proof, a manufacturer or service provider must produce documents demonstrating its due diligence in exploring accessibility and achievability, as required by parts
6,
7, or 14 of this chapter throughout the design, development, testing, and deployment stages of a product or service. Conclusory and unsupported claims are insufficient to carry this burden of proof.