What are some reason to be denied entry into the United States at the airports port of entry?

Border Patrols are always on the look out for the following, false documents, fake ID’s, incomplete papers, the visitor does not look like the person in the pictures, transporting illegal items, may have a contagious decease or acting deranged. If they are using a K1 Fiancee visa and questioned about what the U.S. Citizen fiances address is, where do they work, what their phone numbers is and do not know or ask to repeat the questions over and over , then these are all red flags and deportation may be to follow?