Ask for a copy of their barn rules and keep your eyes open. If you see something that makes you uneasy ask about it. If there are particular things you like to do with your horse make sure they are allowed at the stable. Plan ahead and ask very specific questions-can I do this, how does this work? Understand that no matter what the BO tells you, they are following the "party line" and it's the boarders who really know what's going on. If there was any way to talk to a few of them, you'd get a better feel for the place.