I suppose that many of you all are too young to remember the last gas-stagflation thing in the late 70 and early 80's but livestock was butchered in their pastures by people who are low enough to do it. Even one case where horses were killed and the hind quarters taken.
So, even though it is hard to think badly of everyone, being cautious of strangers, even one professing to interested in buying is a good idea. As much as possible, keeping the stock in view is good but I would also post signs for anyone lucky enough to have stock guard dogs. Just to let them know that they might find easier pcikings elsewhere.