They say they're out of the country on a mission trip and are OK renting the place out below market to a responsible person (faith preferred but not required) who will take good care of it. Then they ask for a "viewing fee" before they send you a code for the non-existent lockbox with the keys.

Source: got to the "send me a viewing fee in itunes gift cards" stage of one of these scams, once. Googled the initial email and it's a common scan template.

The same as orthographic mistakes in postings or scam emails. They filter for more naive and gullible people.

The kind that is trying to build trust with religious people.