Hello @Sara606,
If you go to your reservations you'll see that the status of the reservation says something like "pre-approval sent".
When you pre-approve a potential guest they get a notification and / or an email signalling the pre-approval.
There's no read or delivery receipt sent to the host to indicate that the guest has actually read the pre-approval notification.
It's then completely up to the guest whether they book, send a message with further questions or simply ignore the pre-approval.
If they ignore it then you'll get a message 24 hours later saying that the pre-approval has expired.
Guests often shop around by enquiring from more than one host so they may get pre-approvals from several hosts.
Steve.