Wondering if it was really a church retreat, or if they told you that so that you wouldn’t hesitate in letting them stay. Not saying that church ladies can’t be messy, but just think about it....if someone can lie about occupancy limits (as some of us deal with) why not lie about the reason you are coming So that your party will be immediately sound acceptable to an owner. We are dealing with some really different guests these days. 

I am very fortunate to have a neighbor who acts as my "security resident".  Mentioning that this person is available in an emergency and implying that they are close by (on site) has led to several cancellations by groups who evidently intended to party and did not want to be observed breaking the house rules. 

Great work, and I do the same and yes have people changed their minds to find a place where they can get away with what they need to get away with.

If possible have conversation with the guest by phone. I think I get a better feel for people when we have spoken rather than emailing. I think speaking with guests also helps them to understand there is a real person who owns the property and it is someone's home so they take better care of it.

Hope this isn't too old of a post to help someone concerning not having someone close by to monitor actions at your home.  I use Ring Doorbell and also have stick up cams around outside of the house, so I am able to view activities outside the house if there are indications that things are going on that shouldn't be.  Of course it needs to be mentioned in your listing there are security cameras on the outside of the house.