@Polly16, many hosts worry about the very same thing. If the guest does not understand how the ratings work, they can give you what they think is a good rating, but the rating actually hurts you.
I know some hosts take some trouble to try to explain about the 5-star rating (usually in the house instructions), but there is no guarantee that guests will read and understand. You never know who will be the guest who mis-understands, and if you try to explain in detail to every single guest, you risk looking "pushy" and getting down-rated for that.
I think hosts eventually settle on just providing the best possible experience (as it sounds like you already do), and (when appropriate) dropping subtle hints. (I think one host likes to end messages with "I hope you are having a 5-star experience!" to get the 5-star idea in their head.)