As many hosts have pointed out it is often vital that a guest understands something in particular about a listing before booking it, and sometimes there may be something slightly different about a certain interaction that needs to be agreed upon.
A couple examples:
1) A guest is arriving the same day another guest is checking out and we need them to confirm that they are willing to arrive a little later than we absolutely require in order to make sure the house is ready for them.
2) A guest with a child asks to book our place. While this fact is apparent to a guest who has looked through our pictures we would like to make sure they are aware that there is beer on tap in our living room and that they are comfortable with that before accepting their request.
These scenarios and others would be nicely handled with a feature that allows the conditional acceptance of a request.
Right now I can Accept, Decline or Send Special Offer. I propose another option be added: Accept With Condition.
This would open a dialog that allows me to enter a condition. The guest receives a message "Confirm Your Stay! Your host would like to confirm your reservation and wants to make sure you're happy with this arrangement." The condition entered by the host is displayed with two buttons: "Confirm" and "Cancel Request".
Confirm completes the booking, Cancel Request cancels request.
When a host sends a conditional acceptance the guest has 24 hours to respond, if they don't their request is cancelled.