Some customers asked why the personalization search code like
query = query.UsingPersonalization(searchCriteria.PersonalizationScope) is included on their site, but they still cannot see the difference between normal search and personalized search.
That is because the personalization configuration must be set up properly before the query (query.UsingPersonalization) can work.
First, you would have to purchase the Personalized FIND service which is separate from Product Recommendation. For this you would need to contact your CSM or account manager to obtain the service. After purchasing, the service desk team will provide the provision, and then the Personalized FIND is checked in the Personalization Portal as shown below. From here you can implement the code and test it. You can follow the document of https://webhelp.optimizely.com/20-2/en/getting-started/personalized-find.htm to test it.