If I made a mistake while entering data, I'd be happy if someone told me they receive emails from me that they probably shouldn't be getting, so I do the same when it's not obvious spam/scam.

same. although, if it's a reservation you're being sent, you can cancel it to let the person know they're using the wrong email (plausible deniability because you don't recognize it, yet are getting a reservation)

How would the person know their reservation is cancelled?

they'd show up for the reservation they made and find that it doesn't exist!