If you are on front office reservation duty how would you use a blacklist?

You would check the Names and Addresses of people applying for a reservation against the blacklist. If you found they were on the blacklist you would not provide them with the reservation they were requesting.

A blacklist is a list of people who, for whatever reason, an organization does not want to do business with.

The reason people could be on the blacklist could be that they had not payed their invoice, been rude to staff, damaged property etc.