Hello @Sally50,
I agree with @Lawrene0. You've a live listing on the site. In that sense you're a professional advertising a service to customers.
This guest made a good faith booking under the conditions you had advertised.
Be professional and acccept the booking.
The money and the convience to you of instant book come with responsibilities.
Keep your listing's conditions up to date because when it's live on the site real people with real expecations and real holiday plans are involved.
Steve.