Experience with a brand and formal manufacturer authorisation are different claims. If authorisation matters for a warranty or corrective-action visit, confirm the service route with the manufacturer rather than inferring it from a list of brands repaired.
What the observation tells you
An independent engineer may offer useful repair services without being appointed to carry out a particular manufacturer's programme. The relevant question is whether the proposed visit meets the requirements of your actual claim and appliance.
A useful next step
Keep the manufacturer's instructions or case reference and clarify who is arranging the visit. Obtain agreement on the scope and payment arrangement before assuming that warranty work has been authorised.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.