Caught potential applicant lying - how do I cancel the showing?

[Ludmila M.]

Hi,

I'm looking for advice on a proper procedure to cancel showing if I caught a potential applicant lying. I pre-screened the caller over the phone but after checking her FB I found out she lied about pets and smoking. The posts were from fall 2016, so technically she can say they don't have the cat anymore and that she and her husband quit smoking, but now I have doubts about these people. 

Given I can't deny their application as I didn't send them one yet, are there any formalities I must follow to cancel the showing? Or do I just call/write to her and inform her about my findings? 

Thank you!