Guests checking in and using the room for a love hotel

This past year we have had quite a few people book in who actually live in our city, We then question why if they live in the area and find that they want a night with an escort. We have started getting wise to this as it is not fair to us or our other guests. We are willing to give their money back but not willing to have illicit behaviour to give us a bad name. Has anyone else found this happening and what is their advice? We live in New Zealand.