What you're doing is natural, and Google understands why you're doing it.
Ultimately, they will serve the page that is most relevant to the searcher.
The keywords in the query, a user's search history, or any other relevant data available on a user's local network can help search engines decide what relevant means.
The outcome of gathering this data is this data is understanding a user's intent. Understanding this helps ensure high likelihood that the page shown to a user matches the reason they're searching for it.
Like I always say...Google ranks pages, not sites!
Just because 2 pages have sections with pieces of the same content does not mean that the pages are duplicative.
You could have a same block of text on the page about your window treatment product or your guide to treating windows.
To me, the word "duplicate content" is a deceiving.
At least within the realm of Google Search.
You'll know when you're doing something wrong when it doesn't feel right :)