"I am looking at the design and development requirements of the standard which, if I read it right relates to the D&D of products rather than services. I am clear about the inputs required, the controls needed and the outputs if a product is being made from scratch. However, if a company receives a request from a customer for one of their ready-made products to carry out a cleaning operation and the only thing the company does is to test samples submitted by the customer to determine which of their existing products is suitable to clean it properly is the testing and recommendation regarded as D&D? This would appear to be little more than assisting the customer buy the right product rather than D&D a new product?
Clause 8.3 is both for the development of products and services. But as far as I understand your organization develops products for cleaning operations. When you develop a new cleaning product clause 8.3 applies. When you test samples with different products in order to give the best advice, you are working around clause 8.2. So, I agree with your interpretation.
The following material will provide you information about design and development: