Nightlatch problems

Yesterday I was called by a customer who had left her property as usual but returned to find her key would not turn. After asking some questions I came to the conclusion the snib had dropped down on the nightlatch i gave her a price to gain entry she said she would ring around first. She rang me back 20 minutes later and asked I was going to smash the lock off I replied that would be a last resort if I can not open it without any damage. she asked me to go round asap to open the door after setting up the tools she was in with no damage and now new keys,happy customer